Biology Š WebTeachers 2010
Life processes All living things carry out seven life processes in order to be classed as 驶alive始. The seven life processes are:
Typical animal & plant cells Animal cell
Functions of the cell parts Cell Part
Movement - moving to access resources
Nucleus
The control centre of the cell. Contains genetic information.
Cytoplasm
Watery, jelly-like liquid that fills the cell. It is where the chemical reactions take place.
Cell Membrane
Controls what enters and leaves the cell.
Cell Wall
Provides support to the cell, helping it to keep it始s shape. It is made from cellulose.
Chloroplasts
Absorb the sunlight energy for use in photosynthesis. They contain the green pigment, chlorophyll.
Vacuole
Stores cell sap, a solution of sugar and salts.
Respiration - using oxygen to produce energy Sensitivity - being aware of the surroundings
Plant cell
Function
Nutrition - obtaining food Excretion - getting rid of toxic waste substances Reproduction - producing offspring Growth - growing to full adult size
LIFE PROCESSES & CELLS Using a microscope & preparing slides Here is a typical example of a microscope you may find in a school laboratory:
To prepare a slide for viewing... (1) Place specimen onto a clean slide. (2) Add stain if necessary (iodine often used for plant cells, methylene blue for animal cells). (3) Slowly lower a cover slip onto the specimen (avoid trapping any air bubbles). (4) Drain off any excess stain from around the sides of the cover slip. (5) Place slide onto stage of microscope. To view a slide using a microscope... (1) Make sure that the objective lens is set to low power. (2) Provide a stream of light up into the microscope via the light source. (3) Place a slide onto the stage and secure it with the stage clips. (4) Look down the eye piece and use the focussing knobs to obtain a clear image. (5) If high power is required, rotate the objective lens disc to a higher setting.
Specialised cells Specialised cells are adapted to carry out a specific role in an organism, that no other types of cell perform. Here are some examples: Nerve cells: carry impulses (signals) from the brain or spinal cord to other parts of the body.
Cells, tissues and organs A group of similar cells form a tissue e.g. muscle cells form muscle tissue
A collection of organs working together form an organ system e.g. the muscle system
A collection of organ systems form an organism e.g. a human
A collection of tissues forms an organ e.g. the heart
Sperm cells: the male gametes (or reproductive cells) of an animal. Designed to fertilise the egg.
Organs
Palisade cells: found on the top side of a leaf and packed with chloroplasts, these plant cells are designed for photosynthesis. Red blood cells: contain haemoglobin to absorb and carry oxygen around the body.
Muscle cells: made of fibres which can contract or relax to cause movement.
CELLS & CELL FUNCTIONS
Organs are made up of different tissues which when put together in a structured way, carry out a specific process in an organism. An organ system is a group of organs working together to perform a complex process in an organism. Some organisms have multiple organ systems to carry out the major functions for survival, whilst other organisms just need certain organs.
Root hair cells: found in the roots of a plant and designed to increase the surface area for greater absorption of water and minerals.
Fertilisation Fertilisation is the fusion of male and female gametes (sex cells). When gametes fuse, the first cell of a new organism is created (the zygote). In living things that reproduce sexually, fertilisation is part of the process of reproduction.
Examples of human organ systems include: circulatory system (moving blood around the body), respiratory (for taking in oxygen and removing CO2), nervous (sending impulses to and from the brain), excretory (removing toxic waste), reproductive (producing offspring), digestive (for breaking down & absorbing food), endocrine (hormone production)
Human life cycle Between the stages of birth and death, humans go through significant physical and mental changes.
Requirements for growth In order to achieve full, healthy growth, particularly between birth and adulthood, humans need the following: • • • •
Correct intake of main food groups Regular exercise A healthy living environment Avoidance of unhealthy substances
Although people are capable of reproducing once they go through puberty, most wait until they are adults before having children. As adults they can usually cope better with the demands of being parents, both emotionally and financially.
From birth to adulthood some of the changes include: • physical maturity - growing to full size • sexual maturity - becoming capable of producing children • mental maturity - reaching peak intellect • emotional maturity - becoming self sufficient and independent.
HUMANS AS ORGANISMS Growth Death is the natural final stage in the human life cycle, when the bodyʼs systems can no longer sustain life. Death can happen at any point in the life cycle due to illness or accidents, but it naturally follows old age. Death When the old age stage is reached, humans may notice even further changes to their physical and mental abilities: • they may shrink in height and muscular size • they're bones may weaken and become more brittle • further reduction in hormone levels may affect some body functions • some may suffer memory loss or a reduction in mental capacity • there may be a reduction in efficiency of major body organs • more prone to illness as immune system deteriorates
Old age
Humans remain at the adult stage for quite some time but may notice changes to their bodies as they age, including: • charges to the skin (lines and wrinkles) • changes to the hair (hair loss, greying, texture) • changes to body composition (muscle loss, fat gain) • reduced physical ability (not as fast, less endurance) • onset of menopause in women.
Joints and Muscles The Skeleton The skeleton performs 3 major functions: • Support - it is the frame that body organs hang off • Protection - parts of the skeleton protect vital organs e.g. skull protects the brain, ribs protect heart & lungs • Movement - the skeleton is attached to muscles via tendons which pull on the bones to make us move.
Where bones meet a joint is formed. There are three main types of joint: • Immovable joints - no movement in the joint e.g. between bones of the skull • Slightly movable joints - some flexibility e.g. between vertebrae in the spine • Freely movable joints - large range of motion e.g. elbow, knee, hip, shoulder Three main types of freely movable joints exist - hinge (e.g. elbow), ball & socket (e.g. shoulder), sliding (e.g. wrist). Within many joints cartilage may be found between the bones to provide protection and act as a shockabsorber during movement. Synovial fluid may also be found within freely movable joints to act as a lubricant. Muscles - bands or bundles of fibrous tissue that have the ability to contract. In freely movable joints such as the knee, muscles may work in pairs called antagonistic pairs, contracting on opposite sides of the bones to produce movement in the joint - when one muscle contracts, the other relaxes. Knee Joint
HUMANS AS ORGANISMS Movement
Tendons - connective tissue that attaches muscle to bone allowing the muscle tissue to pull on the bone and so produce movement at a joint. Ligaments - tough connective tissue that attaches bone to bone providing strength and stability at a joint.
The roles of the heart and circulation The more you move, for example during exercise, the greater the energy requirement of your muscles. In order to release more energy from stored glucose, the muscles must have a greater amount of oxygen. To achieve raised oxygen levels, your breathing rate increases, as does your heart rate. Your lungs work harder to take in more Oxygen from the air (and get rid of extra CO2) and your heart works harder to pump blood around the body faster, to supply the muscles with the Oxygen they require. After exercise your heart rate remains high as does your breathing rate, in order to remove the toxins and waste products of respiration. Your heart and breathing rates then steadily return to normal (more quickly the fitter you are).
Lung Structure The lungs are a pair of organs in the chest that are responsible for breathing, allowing blood to pick up oxygen from the air. Movements of the ribs, rib muscles and diaphragm allow air into and out of the lungs. When you breathe in, air passes from your nose or mouth, through the windpipe (trachea) and into one of the two airways (bronchi) which enter the lungs. These airways divide to form smaller tubes (bronchioles), at the end of which are millions of tiny air sacs (alveoli). It is here that oxygen is absorbed from the air, and passes into the bloodstream to be circulated around the body. At the same time carbon dioxide in the blood passes into the alveoli to be breathed out. The lungs are surrounded by a protective lining that consists of two membranes called the pleura.
Inhaled and Exhaled Air When compared, the proportions of the gases in inhaled air and exhaled air are different: Gas
Inhaled air
Exhaled air
21%
17%
0.04%
4%
78%
78%
Oxygen Carbon Dioxide Nitrogen
The air we breathe out has less oxygen, more carbon dioxide, but the nitrogen remains the same. There is also more water vapour in exhaled air. These changes are due to the process of respiration in the cells of the body.
Aerobic Respiration
HUMANS AS ORGANISMS Breathing & Respiration
GLUCOSE + OXYGEN Alveoli
Respiration is a chemical reaction that happens in all living cells. It is the way that energy is released from glucose, for our cells to use to keep us functioning. Glucose and oxygen react together in the cells to produce carbon dioxide and water. The reaction is called aerobic respiration because oxygen from the air is required for it to work. Energy is released during the reaction. CARBON DIOXIDE + WATER + (ENERGY)
Transportation of Reactants & Products The reactants and products of aerobic respiration are transported around the body by the circulatory system.
Alveoli - Oxygen and carbon dioxide are exchanged between the air and blood in the air sacs (alveoli). The alveoli have a large surface area, their walls are thin and moist and they have a good blood supply, which makes them more efficient for gas exchange. The gases move by diffusion into and out of the blood.
Small food molecules produced during digestion can be absorbed across the wall of the small intestine into the bloodstream. Glucose is carried round the body dissolved in plasma, the pale yellow liquid part of our blood. The dissolved glucose can diffuse into the cells of the body from the capillaries. Oxygen that has diffused into the blood through the alveoli is not carried in the plasma, but is carried by the red blood cells. These contain a red substance called haemoglobin, which joins onto oxygen and carries it around the body in the blood. Like glucose, oxygen can diffuse into cells from the capillaries. The carbon dioxide produced during respiration diffuses out of the cells and into the blood plasma. The blood transports it to the lungs. It then diffuses across the walls of the alveoli and into the air, ready to be breathed out.
Balanced Diet
Examples of Vitamins & Minerals
A balanced diet contains the different nutrients in the correct amounts to keep us healthy. Certain foods are not necessarily 'bad' for us, but eating too much of them could be and, in general, too much of any food can give rise to health problems. Eating a balanced diet should prevent overeating and so less food should be stored around the body, reducing the risks associated with weight gain and obesity. The main nutrients required in a balanced diet are shown in the table below: Nutrient
Function
Example Sources
To provide energy
Bread, pasta, cereals
Protein
For growth and repair
Meat, fish, dairy products
Fat
For energy and insulation
Butter, nuts, oil
Vitamins
To maintain health
Fruit, vegetables, dairy products
Minerals
To maintain health
Fruit, vegetables, dairy products, salt, liver
Fibre
To keep food moving through the gut
Cereals, vegetables
Water
For cells and body fluids
Water, milk, fruit juice
Carbohydrate
Not everybody needs the same diet. We need different quantities of each nutrient in our diet depending on our age, health and the lifestyle we lead. The nutritional requirements of a young child will be vastly different from an olympic athlete or a pregnant woman.
Name
Function
Sources
Signs of Deficiency
Eyesight, growth, appetite
Liver, carrots, leafy green vegetables, cod-liver oil
Night blindness
Making red blood and nerves
Fish, meat, milk
Poor nerve function
Vitamin C
Immune system & healing
Fruits and vegetables
Scurvy, poor healing
Vitamin D
Strong bones and teeth
Sunlight, fish, milk
Unhealthy teeth, rickets
Strong bones & teeth
Dairy products, vegetables
Weak bones & teeth
Iron
Red & white blood cells
Red meat, veg, grains
Tiredness, anaemia
Zinc
Immune system
Meat, grains, shellfish
Lesions on skin, poor healing
Vitamin A Vitamin B12
Calcium
HUMANS AS ORGANISMS Nutrition - Diet & Food
Food Tests Test for Starch
Test for Simple Sugars
Deficiency of Nutrients Food provides us with the energy to keep our bodies working and the raw materials to grow and to repair our bodies. A diet lacking in certain nutrients can give rise to various health problems due to deficiency. For example, fibre is needed to keep food moving through the intestines easily, and people who have a fibre deficiency in their diet may get constipation. If your diet lacks carbohydrates you may feel tired or lack energy whilst lack of protein intake may lead to muscle breakdown as the body acquires the protein it needs from its own supplies. As shown in the table above, people with iron deficiency may get anaemia and have too few red blood cells, whilst iodine deficiency may cause a swelling in the neck called a goitre. Vitamin A deficiency can cause blindness. Vitamin C deficiency causes scurvy, which makes the gums bleed, and vitamin D deficiency causes rickets, which can lead to brittle bones and abnormal bone growth in children.
Digestion
How Enzymes work in Digestion Enzymes are special proteins that can break large molecules into small molecules. Different types of enzymes can break down different nutrients: * carbohydrase or amylase enzymes break down starch into sugar * protease enzymes break down proteins into amino acids * lipase enzymes break down fats into fatty acids and glycerol. For example:
Digestion starts in the mouth where the food is chopped up by the teeth and mixed with saliva, which contains enzymes to break down carbohydrate. The ball of food is swallowed and muscles push it down the gullet to the stomach. Food is stored in the stomach whilst enzymes break down the protein. Stomach acid keeps the pH low for the enzymes to work and to kill bacteria. On the way into the small intestine more enzymes are added from the pancreas and the liver. In the small intestine more enzymes are added to digest proteins, carbohydrates and fats. Food is absorbed through millions of villi which cover the gut wall, into the blood stream. Undigested food material moves on into the large intestine where water is absorbed. The remaining material is stored in the rectum ready for egestion from the anus.
HUMANS AS ORGANISMS Nutrition - Digestion Assimilation
Absorption Digested food molecules are absorbed in the small intestine. They pass through the wall of the small intestine and into the bloodstream. Once in the bloodstream, the digested food molecules are carried around the body to where they are needed. Only small, soluble substances can pass across the wall of the small intestine. The inside wall of the small intestine is lined with tiny villi which protrude and give a large surface area. The walls of the villi are very thin so that absorption happens quickly. The villi also contain blood capillaries to carry away the absorbed food molecules.
Soluble food molecules are carried by the bloodstream to all parts of the body, where they are used for growth, energy and maintenance.
Egestion Solid waste is stored as faeces in the rectum and is egested from the body (removed from the body) via the anus.
Changes during Adolescence (Puberty) Puberty usually occurs between the ages of about 10 and 16 but it can start earlier or later for some people. Puberty is controlled by chemicals (sex hormones) from the brain and the sex organs. During puberty, girls and boys go through a series of physical, behavioural and emotional changes which make them sexually mature and capable of having their own children. Physical Changes Both sexes experience an increase in height, growth of hair under the arms and pubic hair growth. Girls and boys also experience physical changes specific to their own sex. Behavioural Changes Girls and boys become attracted to the opposite sex. Girls become more maternal and boys become more aggressive. Emotional Changes Both sexes become more independent and want more freedom from their parents. They also take on more responsibility for their behaviour.
Physical changes in girls Breasts develop Hips widen Periods start (Menstruation)
HUMANS AS ORGANISMS Reproduction - Puberty
The Menstrual Cycle When a girl goes through puberty her reproductive system includes a cycle of events called the menstrual cycle (period). It lasts about 28 days, but it can be slightly less or more than this. The cycle stops while a woman is pregnant. These are the main features of the menstrual cycle: ➡ The start of the cycle, day 1, is when bleeding from the vagina begins. This is caused by the loss of the lining of the uterus, with a little blood. This is called menstruation or having a period. ➡ By the end of about day 5, the loss of blood stops. The lining of the uterus begins to re-grow and an egg cell starts to mature in one of the ovaries. ➡ At about day 14, the mature egg cell is released from the ovary. This is called ovulation. The egg cell travels through the egg tube towards the uterus. ➡ If the egg cell does not meet with a sperm cell, the lining of the uterus begins to break down and the cycle repeats. If the egg cell meets and joins with a sperm cell, it is fertilised. It attaches to the lining of the uterus and the woman becomes pregnant.
Physical changes in boys Penis and scrotum grow larger Muscles develop in chest and shoulders Voice deepens Hair grows on face
A girl starts having periods when she reaches puberty and she will have a period every month until the menopause (usually in her 40s or 50s) when periods stop altogether. If she gets pregnant, her periods temporarily stop until she has had the baby and then start again some time afterwards, when her system has returned to normal. Girls may experience some physical discomfort and raised emotions just before each period.
Female Reproductive System Front view
Hostile environment The vagina is a hostile environment for sperm, producing acids which can harm them and prevent them from swimming up through the cervix. In order to combat this, semen contains an alkali to neutralise the acid produced by the vagina and allow sperm to survive. Front view
Uterus Also known as the womb, this is where the embryo develops into a baby. Ovaries These contain the eggs (ova) and alternately release one each month into the oviducts. They also produce key female hormones Oviducts (Fallopian Tubes) These tubes connect the ovaries to the uterus. Fertilisation of the egg takes place here if sperm are present. Vagina This receives the penis during intercourse and acts as the birth canal when the baby is ready to be born.
HUMANS AS ORGANISMS Reproduction - Systems
Male Reproductive System Penis This is designed for passing urine from the bladder and semen, containing sperm, from the testes. It is capable of becoming erect in order for intercourse to take place. Testes These are held in a sac called the scrotum and produce sperm and the hormone testosterone. Vas Deferens These sperms ducts carry sperm from the testes to the urethra. Urethra This tube runs through the centre of the penis to carry semen and urine out of the body. Seminal Vesicle, Prostate & Cowper始s Glands These add nutrients and fluid to sperm to make semen.
Side view
Sex Hormones The changes at puberty are under the control of the sex hormones, progesterone and oestrogen in girls and testosterone in boys. These hormones continue to play major roles in the menstrual cycle and pregnancy and in the production of sperm, after puberty. Side view
Making Babies
Fertilisation
In order to create a new person, fertilisation of the ova (egg) must occur. Fertilisation happens when a male gamete (sperm cell) meets with the female gamete (egg) and joins with it. This happens after sexual intercourse (copulation) in which a man puts his penis into the woman's vagina. Stimulation of the erect penis causes semen to be released (ejaculation). Sperm cells travel in semen from the penis and into the top of the vagina. They enter the uterus through the cervix and travel to the oviducts (Fallopian tubes). If a sperm cell meets with an egg cell there, fertilisation can happen. This is the start of the creation of a new person.
Copulation or sexual intercourse delivers the male gametes (sperm) to the female reproductive system, where fertilisation may occur.
HUMANS AS ORGANISMS Reproduction - Making a new Person
The Zygote, Genes & Characteristics
Male and female gametes (sperm & egg) each carry one half of the genetic information needed to create an individual. The sperm cell has 23 chromosomes in its nucleus from the father and the egg has 23 chromosomes in its nucleus, from the mother.
When the gametes join and their nuclei fuse (fertilisation), a zygote is formed. The zygote has one complete set of genetic information, 46 chromosomes,
The zygote keeps dividing to produce a large number of cells and eventually a foetus, which continues to develop into a new person.
Eventually a new baby is born, which displays characteristics inherited from its parents. Examples of inherited characteristics are gender, eye colour, hair colour, skin colour, lobed or lobeless ears, inherited diseases and blood group.
Development of the Foetus
What happens at Birth?
Foetal development from 8 to 40 weeks
Foetus
The foetus relies upon its mother as it develops. It requires protection, oxygen and nutrients (food and water). It also needs its waste substances to be removed. The foetus is protected by the uterus and the amniotic fluid, a liquid contained in a bag called the amniotic sac or amnion.
The Role of the Placenta The placenta provides the foetus with oxygen and nutrients, and removes waste substances. It grows into the wall of the uterus and is joined to the foetus by the umbilical cord. The mother's blood does not mix with the foetus's blood, but the placenta lets substances pass between the two blood supplies. Oxygen and nutrients diffuse across the placenta from the mother to the foetus whilst waste substances, such as carbon dioxide, diffuse across the placenta from the foetus to the mother.
HUMANS AS ORGANISMS Reproduction - The Foetus & Birth
Late in the 9th month of pregnancy, the unborn baby will start to move to get ready for birth. Usually, this is head first. A mother's "water breaking" may be one of the first signs of labor. This happens when the amniotic sac, which holds and protects the unborn baby, breaks open. Then, some of the fluid drains through the cervix and out the vagina. As the muscle contractions of the uterus get stronger, the cervix opens (dilates) and the unborn baby's head can push down into the vagina. (The vagina is also called the "birth canal.") The contractions become stronger and more often, and the cervix opens 10 centimeters (4 inches) wide. During a normal birth the baby's head appears first. Then the shoulders turn and more contractions push the baby out. Sometimes a birth through the vagina may not be possible or recommended. This can be because the doctor has some worries about the health of the mother or the baby. In this case, a Cesarean section (C-section) is usually done. This is a type of surgery in which a cut is made in the mother's abdomen and uterus. Then the baby is removed. Delivery is finished when the baby is outside the mother's body. The placenta and other fetal tissue (called afterbirth) are delivered just a little while later. The baby's mouth and nose are cleared of mucus. The baby breathes and cries. Then, the baby is usually given to the new mother. After the delivery, the umbilical cord is clamped and cut. This separates the baby from the placenta. The umbilical cord will dry and heal to form the belly button (navel).
The Effects of Smoking Smoking damages your health. It causes diseases ranging from lung cancer, bronchitis and emphysema to heart disease, which are all major killers in the UK. Tobacco smoke contains many harmful substances including tar, nicotine and carbon monoxide. Tar causes cancer of the lungs, mouth and throat. It coats the surface of the bronchioles and the alveoli which causes coughing and damages the alveoli, making it more difficult for gas exchange to take place. Tar also damages the cilia cells lining the bronchioles which prevents the mucus from being removed. This leaves the individual more prone to infection and causes coughing. Nicotine is addictive causing a smoker to want more cigarettes. Nicotine also increases the heart rate and blood pressure, and narrows blood vessels which can lead to heart disease. Carbon monoxide reduces the amount of oxygen that the blood can carry. The circulatory system has to work harder, which can lead to heart disease.
The Effects of Drugs Drugs are substances that affect the body. Medicines are drugs that help people when suffering from pain or disease. Other drugs, known as recreational drugs, are taken by some people for pleasure. Some recreational drugs are legal, such as tobacco, alcohol and caffeine. Most other recreational drugs are illegal, such as cannabis and heroin. Any drug that is misused can cause damage to the body and may cause other problems. All drugs can damage the liver, because it is the liver that breaks drugs down in the body. Injecting drugs using shared needles may lead to diseases such as HIV and hepatitis, due to infected blood. Recreational drugs are addictive, and they may be depressants or stimulants. Depressants slow down messages in the brain and nerves e.g. alcohol, solvents, cannabis, heroin. Effects of depressants include feelings of well-being, lowered inhibition, slowed thinking & muscular activity, hallucinations. Depressants can cause long-term damage to the liver, brain and heart. Stimulants speed up messages in the brain and nerves e.g. caffeine, amphetamines, cocaine and ecstasy. Effects of stimulants include making you feel more energetic and confident, but they can damage the liver and heart. They can also cause loss of memory and concentration, and bring a greater risk of mental illness.
HUMANS AS ORGANISMS Health - Substances Affecting Health
Positive Influences on Health Staying healthy is clearly influenced by what you do with your body and what you put into it. Harmful substances can damage your body and so misuse of any kind of drug is going to have detrimental effects. The food you consume also plays a vital role in your health. The right amount of nutrients from the right types of foods can promote good health and correct functioning of your body始s organs. Conversely, over indulgence in the wrong types of foods can lead to weight gain, heart disease and other associated illnesses. Exercise also affects your health, promoting muscle tone and efficient cardiorespiratory function (heart and lungs). Regular exercise also reduces excess fat storage and delays the onset of aging. A fitter person is generally a healthier person.
Microbes Microbes are micro-organisms that can only be viewed using a microscope. There are three main types of microbe: fungi, bacteria and viruses. Fungi Not all fungi are microbes as some are multicellular organisms. Yeasts are single-celled fungi, so they are microbes. Fungi are usually the biggest type of microbe. Bacteria Bacteria are usually smaller than fungi. Bacteria have many different shapes. Some have flagella (tails) that allow them to swim. Viruses Viruses are the smallest type of microbe. A virus can only reproduce inside a cell.
How are Microbes Spread? Microbes can be spread through the air, through touch, through contaminated food, in water and through contact with animals. Air People sneezing or coughing can transfer droplets containing microbes into the air and these can be breathed in by other people, infecting them. Colds, flu, chicken pox and TB are examples of infections spread by air. Touch Microbes can be spread by physical contact with an infected person or by touching surfaces touched by an infected person. Athlete始s foot is spread in this way. Food Poor handling or under-cooking of food can leave harmful microbes on them when eaten e.g. salmonella Water Dirty, untreated water can contain microbes which get into the body when the water is swallowed e.g. cholera Animals Microbes carried by animals can infect a person who is bitten or scratched e.g. malaria
Harmful Microbes Some microbes cause diseases which can make humans very ill or even kill them. Other microbe infections can cause effects such as skin rashes or a general feeling of being unwell, which are uncomfortable but not life threatening. Type of Microbe
Examples of Diseases
Fungi
Athlete始s foot, Thrush
Bacteria
Salmonella, Tuberculosis, Typhoid, Tetanus, Plague, Dysentery, Cholera
Viruses
Common cold, Flu, Chicken pox, Mumps, Measles, AIDS, Hepatitis, Rabies
A person is infected when microbes enter the body and are able to reproduce in the body. They produce harmful toxins and damage tissues and organs.
HUMANS AS ORGANISMS Health - Microbes & Disease
Not all Microbes are Harmful Although microbes are associated with disease, some are very useful and indeed some are vital to our health. Bacteria living in our digestive system are very important in the correct functioning of our intestines in the digestive process. Bacteria are involved in the decomposition of waste materials on earth. Certain bacteria cause changes in milk which make yogurt and cheese. Yeast cells are also used to make bread and alcoholic drinks, as they turn sugar into CO2 (which makes the bread rise) and alcohol.
Defence against Microbes
Natural Barriers The body has some natural barriers to prevent microbes entering. These include the skin, scabs (to block up cuts), acid in the stomach and mucus in the lungs. Human Immune System Your immune system kills microbes that get past the natural barriers. White blood cells are the key; some engulf and kill microbes whilst others produce antibodies which kill microbes or cause them to stick together, making them easier to kill.
Fighting Microbes with Medicines Antibiotics If you have a serious infection caused by bacteria, you may be given antibiotics to help fight the infection. Some antibiotics stop the bacteria reproducing and others kill the bacteria. Immunisation against Infections e.g. Tetanus, Mumps, TB Immunisation involves injecting a person with a vaccine. Vaccines contain a weak form of the disease-causing microbe, or some of its antigens. The immune system then responds by producing white blood cells with the correct antibody to kill the microbe, so you become immune without getting ill. If you then get infected with the disease, your body already has the white blood cells to fight it.
Requirements for Plant Growth
Photosynthesis
In order to survive and grow properly, a plant needs to obtain several things: • • • •
Plants produce their own food by capturing and using Sunlight energy. This is achieved using the process of photosynthesis: # SUNLIGHT CARBON DIOXIDE + WATER GLUCOSE + OXYGEN
Carbon Dioxide Water Light Minerals
CHLOROPHYLL
• •
Plants obtain these components in different ways. Carbon Dioxide This is absorbed from the air through tiny holes on the underside of leaves. These tiny holes are called stomata (singular: stoma). The CO2 diffuses through the stomata into air spaces between the cells. CO2 is then used as a reactant in the process of photosynthesis. Light Sunlight is absorbed by the chloroplasts in the cells of a leaf. Chloroplasts contain the green pigment chlorophyll which captures the light energy and uses it to power the process of photosynthesis. The cells in the top layer of leaves (palisade layer) are packed with chloroplasts to make the process more efficient.
• • •
Light is captured by the chlorophyll in the chloroplasts of leaf cells. Chlorophyll is the green pigment in the Chloroplasts of a plant cell, so only cells containing chloroplasts will photosynthesize. The glucose produced during photosynthesis is then used in respiration to produce energy. During photosynthesis, oxygen is produced as a waste product and released into the air by the plant. Photosynthesis can only happen during the daytime - a plant doesnʼt photosynthesise at night.
GREEN PLANTS AS ORGANISMS Nutrition and Growth
Water Water is needed as a reactant in photosynthesis and to keep the plant turgid. A plant without enough water will wilt. Water is absorbed through the root hair cells in the roots.
The Role of Root Hair Cells Minerals Plants also need elements such as nitrogen, phosphorus and potassium. These are needed to allow the plant to make other substances e.g. nitrogen for proteins. Soil contains minerals made up of these elements, dissolved in water, e.g. nitrates, phosphates etc. Plants absorb the minerals from the soil water, through their root hair cells. Fertilisers are sometimes used to ensure the soil has minerals for plant growth.
• • •
•
Root hair cells are used by a plant to obtain water and minerals from the soil. They are specialised cells designed for that particular function. Root hair cells have a large surface area and very thin walls and so are more efficient for absorbing water and minerals. They have no chloroplasts because they are found in the roots under the ground.
Plant Respiration
Respiration-Photosynthesis Balance
Plants need to respire in order to produce energy to: • Grow • Take in minerals • Move • Make specialised cells
• • • •
The food (glucose) a plant produces during photosynthesis is used in the process of respiration, which releases the energy from the glucose: GLUCOSE + OXYGEN
•
Plants, being living things, respire all the time, day and night. They only photosynthesise during the day, when there is light available. Therefore, at night, they are not producing oxygen. During the day, the amount of oxygen produced by photosynthesis is massive compared to the amount the plant uses for respiration. Plants that lose their leaves in winter store food produced during the summer by photosynthesis. They store enough food to last them over winter, and to provide energy reserves for new growth in the spring.
CARBON DIOXIDE + WATER + (ENERGY)
The energy produced in respiration is used by the plant to grow and to provide its other requirements. Respiration happens all the time, whether it is dark or light (unlike photosynthesis, which only happens in the day). As with all living things, Carbon Dioxide is produced as a waste product. Water is released (evaporates) from the stomata as part of the process of transpiration, shown below:
GREEN PLANTS AS ORGANISMS Respiration
The Carbon Cycle All living organisms are made up of molecules that contain carbon: carbohydrates, proteins and lipids. The carbon cycle includes all the reactions that allow living organisms to use carbon to manufacture their tissues and release energy. Plants are the starting point of the carbon cycle. Through the process of photosynthesis, plants absorb carbon from the air (CO2) and incorporate it into their biomass (leaves, wood, roots, flowers, fruits). This organic matter provides food for other organisms (consumers). By releasing energy when they respire, living things return carbon to the atmosphere in the form of CO2.
Conditions
Respiration Photosynthesis Balance
Dark
Respiration but no photosynthesis
Dim Light
Rates of photosynthesis & respiration are equal
Bright Light
Rate of photosynthesis much greater than respiration rate
Parts of a Flower
Stages of Reproduction
2. Fertilisation
The reproductive organs of a flowering plant are in the flower.
The stages of reproduction in a flowering plant are as follows:
Once pollen has been transferred to the stigma, a pollen tube grows down through the style, into the ovary and into an ovule. The male nucleus travels down the pollen tube and fuses with the female nucleus to form a zygote. This is fertilisation.
1. 2. 3. 4.
Pollination - transfer of pollen Fertilisation - fusion of male and female sex cells Seed dispersal - spreading of seeds away from the plant Germination - growth of a seed into a new plant
1. Pollination This is the process in which pollen is transferred from the anther of a flower to the stigma of the same (self pollination) or another (cross pollination) flower. This transfer of pollen can be made by the wind or by visiting insects.
GREEN PLANTS AS ORGANISMS Reproduction in Flowering Plants
3. Seed Dispersal After fertilisation, the fertilised ovule develops into the seed and is housed in the ovary which develops into the fruit. Seeds can be dispersed in a number of different ways. They may be carried by wind, water or animals. Some plants even shoot the seeds out explosively. Spreading the seeds as far as possible away is important because if the seeds are not dispersed, many germinating seedlings will grow very close to the parent plant. This results in competition for resources (light, water, nutrients) between every one of the seedlings as well as with the parent plant.
4. Germination Carpel The female reproductive organ made up of the stigma (sticky for pollen to stick to), the style (connecting the stigma to the ovary) and the ovary (contains the female sex cells inside ovules). Stamen The male reproductive organ made up of the anther (contains the pollen - male sex cells) and the filament (supports the anther). Petals Flowers usually have colourful petals to help attract insects for pollination.
This is the first stage in the growth of a seed. When the conditions are right (enough warmth, enough moisture), a root will emerge from the seed coat, followed eventually by the first shoot.
What is Variation? Variation is the difference between organisms. Different species have completely different genes and so are completely different to other species of organism e.g. a cow is totally different to a rose bush. But you also get variation within a species. For example, humans have differences in skin colour or blood group. Continuous Variation This is the type of variation where a feature can vary over a wide range of values. Examples of features showing continuous variation are weight, intelligence, leaf size, height etc. which can vary continuously over time. Discontinuous Variation This is the type of variation where a feature can only take particular values. Examples of features displaying discontinuous variation are blood group, natural hair colour, eye colour etc. which can only take distinct values and donʼt change over time.
Environmental & Inherited Variation Some variation within a species is inherited, and some variation is due to the environment. Environmental Variation Characteristics of animals and plants can be affected by environmental factors and ʻupbringingʼ e.g. climate, dangerous areas, diet, soil conditions, lifestyle. Variation in characteristics as a result of the surroundings is called environmental variation. Examples of this are weight, plant size, religion, flower colour, language etc. Inherited Variation People have similar physical features to their parents, but they will not be identical to either of them. This is because they get half of their inherited features from each parent; half of their genetic information came from the motherʼs egg and half from the fatherʼs sperm. Variation in characteristics, as a result of inheritance from the parents, is called inherited variation. Examples of this are eye colour, skin colour, gender, blood group, shape of ears etc. Some features display variation due to a mixture of inherited and environmental factors e.g. identical twins have identical genes (inherited) and so look the same, but different diets may produce a fat twin and a skinny twin (environmental).
VARIATION, CLASSIFICATION & INHERITANCE Variation & Inheritance
Selective Breeding Natural Selection Natural selection is the process whereby a species evolves over time, inheriting the features best suited to the environment in which the species lives. Over time the best genetic features most useful for survival and reproduction are passed on to their offspring. Less useful features may be less evident eventually and may even disappear altogether. Natural selection may result in a species changing appearance or even evolving into a new species, given enough time.
Artificial Selection Artificial selection is where humans try to develop particular varieties of animals or plants that display useful characteristics. The animals or plants from existing stock that show the best required characteristics, are selected for breeding purposes. The resulting offspring producing the best characteristics are then used for breeding again - the process is repeated until the exaggerated characteristics required are obtained. Examples of artificial selection: • • •
High yield milk or beef cattle Disease or frost resistant crops Pedigree dogs
Taxonomic Groups Although species can be very different from each other, many of them have similar features that allow us to put them into groups. Putting different species into different groups according to their features is called classification. All living things can firstly be grouped into five kingdoms:
Each kingdom is then divided into further groups, e.g. breakdown of animal kingdom:
Protista Animals
Monera Living Things
Fungi Vertebrates
Plants
Invertebrates
Fish -- Amphibians -- Reptiles -- Birds -- Mammals
Animals Protista are single celled organisms Monera are bacteria and blue-green algae
Annelids -- Arthropods -- Coelenterates -- Echinoderms -- Flatworms -- Molluscs
VARIATION, CLASSIFICATION & INHERITANCE Classification
Using Keys for Identification A key is a list of clues and answers for identifying which species an organism is. Take one organism at a time and work through the questions for that organism only until you end up with the name of the species. Here is a simple example:
Features of Vertebrates Vertebrate group
Q1. Does it have a backbone?
Yes...Go to Q.3 No....Go to Q.2
Q2. Does it have legs?
Yes...Itʼs an ANT No....Itʼs a WORM
Q3. Does it have fins?
Yes...Itʼs a FISH No....Go to Q.4
Q4. Does it have feathers?
Yes...Itʼs a BIRD No....Itʼs an ELEPHANT
Features
Fish
Scales, gills, fins, cold blooded
Amphibians
Smooth, damp skin, lay eggs in water, live on land and in water, cold blooded
Reptiles
Dry scales, lay soft-shelled eggs on land, cold blooded
Birds
Feathers on body, wings, lay hard-shelled eggs on land, warm blooded
Mammals
Hair or fur on body, produce milk, give birth to live young, warm blooded
Protecting the Environment
Habitats
It is important to protect the environment so that it continues to support all the organisms that live in it. There are many ways that the environment can be protected. Changes caused by humans and their activities can be limited by sustainable development. This involves making sure that any change in the environment for the benefit of humans causes minimal damage to other species and leaves sufficient natural resources to provide for the future. The following are examples of sustainable development:
The place where an organism lives is called its habitat e.g. woodland, pond. The conditions in a habitat are called the environment e.g. the temperature, amount of rainfall etc. Plants and animals develop certain features or characteristics over millions of years, which allow them to live successfully in their habitats. These features are called adaptations and we say that the living thing is adapted to its habitat. Depending on the habitats involved, living things have to adapt in different ways.
• • •
creation of nature reserves, where animals and plants are protected from hunting and other human activities reduction of pollution by using less fossil fuel and being ʻgreenerʼ in everyday life (reducing carbon footprint) protection of fish populations by setting fishing quotas, so limiting the number of fish that can be caught
Factors Affecting Population Size A population is the number of a particular species in a habitat. All the different species of animals and plants living in a habitat form a its community. The organisms in a community compete for the resources available i.e. animals compete for food, water and space whilst plants compete for light, water, space and minerals. Animals that get more resources are more likely to survive and their population to grow than animals who get fewer resources. Plants growing in a location that limits their resources e.g. a small plant growing under a tree, are less likely to survive than those growing in a location with plentiful resources e.g. the same plant out in the open. This is why you are less likely to find a large population of small flowers such as dandelions growing in a shaded, woodland area.
LIVING THINGS IN THEIR ENVIRONMENT Adaptation & Competition
Daily and Seasonal Changes Some habitats do not stay the same all the time. Examples of daily changes to the environment include: • changes in light and temperature from day to night • changes in water level, in accordance with tides Examples of seasonal changes to the environment include: • changes in temperature and weather • changes in hours of daylight • changes in quantities of vegetation Examples of organisms adapting to seasonal changes include birds migrating, trees losing their leaves, animals storing food, hibernation, animals growing thick coats etc.
Examples of Adaptation Here are some examples of organisms adapting to their environments: Camel Camels live in deserts, so they have to cope with conditions that are hot and dry during the day and cold at night. To c o p e w i t h t h e environment camels can store lots of water, they lose very little water, they can cope with large differences in temperature, they have wide, flat feet to help them walk on the sand and they have slit-like nostrils and two rows of eyelashes to help keep the sand out. Cactus Cacti also live in deserts and so cope with the environment by having no leaves and a small surface area to reduce water loss, they store water in their stems, they have shallow but long roots to absorb water quickly and they have spines to protect themselves from being eaten by herbivores. Polar Bear Polar bears live in the arctic and are adapted to arctic conditions by having black skin to absorb heat well, they have a white appearance for camouflage, they have thick layers of fat and fur for insulation and they have big feet to spread the weight on snow or ice.
Food Chains
Food Webs
A food chain shows the different organisms that live in a habitat, and what eats what. Food chains always start with a producer, which is an organism that makes its own food, and end with a consumer, which is an animal that eats a plant or another animal.
A food web is made up of all of the food chains in a habitat linked together.
Periwinkle
Moth
Frog
Snake
Hawk
In the above example of a food chain, the periwinkle is the producer, because it makes its own food (through photosynthesis), the moth is the primary consumer (and is a herbivore), the frog is the secondary consumer, the snake is the tertiary consumer and the hawk is the top carnivore or top predator (at the top of the food chain). The arrows mean ʻis eaten byʼ. A predator is an animal that eats other animals, and the prey is the animal that gets eaten by the predator.
LIVING THINGS IN THEIR ENVIRONMENT Feeding Relationships
Accumulation of Toxins in Food Chains Toxins are poisonous materials, some of which break down quickly into harmless substances in the environment. Other types of toxins do not break down and instead accumulate in the food chain and damage the organisms in it, and in particular the top carnivores. A toxin entering the food chain at the lowest level may seem to have a very low concentration, but as the larger organisms higher up the food chain eat more and more of the contaminated organisms lower down, so the concentration of toxins builds. Over time, the concentration of toxins in the top carnivore is high, as this organism has eaten many of the consumers below it in the food chain. Examples of this accumulation of toxins can be seen in food chains affected by substances such as mercury (in some paints) and the insecticide DDT. Plant plankton contaminated by mercury pass on their contamination up the food chain - plant plankton are eaten by animal plankton, which are eaten by small fish. Larger fish e.g. tuna eat the small fish. These top carnivores contain a high level of mercury from all of the organisms eaten below them in the food chain. Mercury damages the nervous and reproductive systems of organisms. A similar thing happens when insects containing DDT are eaten by small birds which are eaten by larger birds. The DDT weakens the eggs of the top carnivore which could lead to them dying out. DDT is now illegal to use.
Problems in one part of the food web can give rise to strange ʻknock-onʼ effects in the rest of the web. For example, in the above food web, if a chemical was used to kill off the insects feeding on the plants, frogs may die out in the habitat as they have no food. Snakes would have less frogs to eat so they would eat more rabbits which would leave less food for foxes. There would be fewer hawks as their food supply would be less, and so on. The ʻknock-onʼ effects of killing off the insects in this food web are huge.