Leaving Certificate Biology Plus

LEAVING CERTIFICATE

Biology

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Edco 2013

LEAVING CERTIFICATE Michael O’Callaghan X A new, exam-focused textbook with student

Chapter 14 Cell division

assessment and exam tracker, written by Michael O’Callaghan, author of the highly successful Leaving Cert Biology

X Written in line with: – recent examination papers – recent interpretations from marking schemes – extensive feedback received from teachers

and students

CHAPTER 7 THE CELL

Learning objectives

HIGHER

To explain the terms ‘cell continuity’, ‘chromosome’, ‘haploid number’ and ‘diploid number’ To describe the cell cycle and cell activities in interphase and mitosis To define the term ‘cancer’ and give two possible causes To define the term ‘mitosis’, explain it simply and identify its main function in single-celled and multicellular organisms To define the term ‘meiosis’ and explain its functions To perform a detailed study of mitosis, with the aid of diagrams.

Cell continuity Cell continuity means that all cells

develop from pre-existing cells.

Cell continuity gives rise to the continuity of life, which was discussed in Chapter 2.

When a new cell forms (from an existing cell) it goes through the following three phases: It produces or synthesises all the materials it will need

It grows larger

It reproduces to form new cells.

THE CELL

Cell continuity implies that most cells spend a lot of time producing the chemicals and substances they need to survive and grow. They are not actively dividing into new cells during this phase of their life. Cells spend a relatively short time engaged in cell division.

Chromosomes When a cell is not dividing, the chromosome s exist as long, thin threads called chromatin. At cell division, chromatin contracts to form a number of clearly distinguishable chromosomes.

Every species has a definite number of chromosomes in each cell. For example, humans have 46 chromosomes in each body cell.

Each chromosome is composed of hundreds, or even thousands, of genes. These genes are arranged along the chromosome as shown in diagram 14.2.

Chromatin

Chromosome

Positions of different genes

At cell division

14.1 A human chromosome (SEM)

Chromosomes are coiled threads of DNA (which forms genes) and protein that become visible in the nucleus at cell division.

Four chromosomes

14.2 Chromatin, chromosomes and genes

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X Syllabus-based and exam-focused throughout

X Includes the latest information on new discoveries in Biology CHAPTER 29 Homeostasis

Summary the outside The external environment surrounds of an organism. the cells in The internal environment surrounds an organism.

X Each chapter includes:

large To improve their rate of exchange, such as: organisms require special features ●● Flat structures a large surface area ●● A respiratory system with systems, which take ●● Respiratory and excretory the body surface. materials from within the body to

Homeostasis: to maintain a ●● Is the ability of an organism constant internal environment organ systems ●● Involves many organs and the brain acting together, co-ordinated by to exchange ●● Often requires an organism materials with its environment.

system Large organisms require a circulatory to carry materials over long distances.

their environment Cells exchange materials with by diffusion, osmosis and active transport.

Homeostasis allows: to function at ●● Cells, and therefore organisms, their most efficient rate of external ●● Organisms to function independently conditions when Slight changes in internal conditions ●●

necessary.

not needed in Special organs of exchange are is adequate. small organisms because diffusion

Revision questions 1 (a) What is homeostasis? and (b) Distinguish between the external internal environment of an organism. for humans. (c) Name the internal environment in homeostasis 2 (a) Name three organs involved in humans. of the (b) Briefly explain the role of each organs you have named. for a (c) State the immediate consequences ceased person if each of the named organs

found in large 3 (a) Why are circulatory systems animals but not in small ones? an organism (b) Suggest one method by which without a circulatory system might transport materials. for temporary 4 ‘Homeostatic mechanisms allow Give two changes in the internal environment.’ examples in support of this statement.

to function.

Exam questions

6 (c)

7 (c)

reason (i) What is homeostasis? Note one body. why it is important in the human (2007 HL Q 15) (i) Explain the term homeostasis. (ii) Homeostasis often requires an organism to exchange materials

Previous examination questions n/a

Higher level 2004 Q 12a 2007 Q 15c 2009 Q 15c 2012 Q 15c biologyplus/examhelp

Latest questions at www.edco.ie/lc

1. Liver.

2. Lungs.

3. Nephrons of kidneys.

(2012 HL Q 15)

Online test and assessment tracker Scan the QR code and test yourself on chapter 29 www.edco.ie/lcbiologyplus

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– learning objectives – revision questions – the most recent examination questions – a summary for quick revision – clear colourful diagrams, photographs and sketches to help students reproduce diagrams in the Biology exam CHAPTER 10 HIGHER LEVEL ENZYMES

In this activity the enzyme used is catalase. This enzyme is obtained by blending celery.

The reaction can be shown as:

Hydrogen peroxide

catalase

2H2O2

catalase

(substrate)

(enzyme)

10.13

– in distinctive panels at the end of each chapter – include suggested results – can be accessed online through

www.edcodigital.ie for teachers and on

www.edco.ie/biologyplus for students or on

FREE DVD which accompanies textbook

Water + Oxygen 2H2O + O2

(products)

The reaction to show the action of the enzyme catalase

1. Place some stalks of celery in a blender and add some water.

Turn on the blender to form a pulp. (Celery contains the enzyme catalase.)

2. Filter the pulped celery into a beaker using coffee filter paper (this will remove the cell parts; coffee filter paper allows faster filtration than laboratory filter paper).

3. Place some of this filtered solution into a large graduated cylinder and place in a water bath at 25°C (this is an ideal temperature for catalase activity).

4. Add some pH 9 buffer solution to the graduated cylinder (this ensures a constant pH; the optimum pH for catalase is 9).

5. Using a dropper add one drop of washing-up liquid (the washing-up liquid traps bubbles of oxygen, causing the formation of foam).

THE CELL

X Mandatory investigations and experiments:

aNd ENERGY CaRRIERS

Activity 11 To investigate the effect of heat denaturation on enzyme (catalase) activity

HIGHER

Ordinary level

between different tissues, or between itself and the external environment by diffusion, osmosis, and active transport. Explain each of the underlined terms. of the (iii) State one way in which each following contributes to homeostasis.

tHe oRGaNism

Section C the role of the 5 (a) What is homeostasis? State kidneys in homeostasis.

(2004 HL Q 12)

Graduated cylinders

Blended celery + pH 9 buffer + washing-up liquid 10.14

Water bath (25°C) Hydrogen peroxide

The effect of heat denaturation on enzyme activity

10. Boil some of the filtered celery solution for 10 minutes (this denatures the enzyme catalase).

11. Repeat steps 3 to 9 using the boiled catalase solution (this acts as a control).

12. Results may be presented as:

6. Add some hydrogen peroxide to a smaller graduated cylinder. Place this in the water bath (hydrogen peroxide is the substrate).

7. Leave both solutions until they have reached 25°C (this ensures a constant temperature).

8. Add the hydrogen peroxide to the blended celery in the large graduated cylinder.

9. Note if foam is produced or not after 2 minutes.

Hydrogen peroxide

Activity 11 results

Foam produced (yes or no)

Unboiled Boiled enzyme enzyme (control)

Foam Celery, pH 9 buffer, washing-up liquid 10.15

Bubbles of oxygen

Investigating the activity of catalase

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ion

CHAPTER 41 Human reproduct

HIGHER

Day 5

few hundred morula forms a hollow ball of a

the Around 5 days after fertilisation, cells called the blastocyst. form the form the trophoblast. This will later The outer cells of the blastocyst (called the The inner cells of the blastocyst membranes around the embryo. embryo. inner cell mass) will later form the uterus. the into tube Fallopian the The blastocyst is pushed down

A blastocyst (or blastula) is a hollow ball of cells formed from a morula.

X An extensive range of definitions included

Morula

Trophoblast Blastocyst

Fluid filled cavity Inner cell mass

microscope) 41.19 Five-day-old blastocyst (light

41.20 Development of the blastocyst

Embryonic development Day 10

the blastocyst the cells of the inner cell mass of About 10 days after fertilisation, mesoderm primary germ layers: the ectoderm, form three layers of cells called and endoderm. is divided into an outer mesoderm) (the cells of layer In humans, the middle called a coelom and it allows space is them between gap The and inner layer. heart, lungs and kidneys to develop. for complex organs such as the Each germ layer gives rise Ectoderm to specific structures in the Mesoderm developing embryo (as shown in the table below). Animals Coelom (such as humans) that arise from three germ layers have Mesoderm more complex organ systems Endoderm Blastocyst than those that arise from only the embryo two cell layers (e.g. jellyfish, 41.21 The three germ layers of which lack a mesoderm).

Embryonic development Germ layer Ectoderm Mesoderm Endoderm

Organ or system produced Skin, nails, hair, nervous system

respiratory system, Muscles, skeleton, excretory system, system circulatory system, reproductive and excretory systems; Inner lining of digestive, respiratory liver and pancreas

X Important terms and

CHAPTER 15 DNA AND RNA

additional explanatory information highlighted throughout

Characteristics are traits or features that are inherited genetically.

It is the expression of genes that produces the characteristics or traits that are inherited. Characteristics such as those listed earlier arise from the interaction between the genes that are inherited (heredity) and the environmen t.

A child may inherit genes for tallness, for instance, but if the child’s diet lacks the correct nutrients, the genes may not be able to cause tallness, i.e. the genes may not be expressed.

Characteristics arise from the interaction of heredity and the environment.

479 THE CELL

ted) cells that can give rise to many Stem cells are unspecialised (undifferentia in red bone found in the blastocyst (and also different types of tissue. They are the use of stem body). Research is ongoing into marrow and other places in the body parts. cells to form, renew or repair damaged

Germ layers are basic layers of cells in the blastocyst from which all adult tissues and organs will form.

tHe orGaniSm

13

Biology In the same way, leaf cells have genes to control the production of the green pigment, chlorophyll. However, if the plant grows in a dark place these genes do not work and chlorophyll is not made.

Chromosomes Chromosomes are composed of about 60% protein and 40% DNA. The protein is responsible for holding the DNA in a tightly packed configuratio n so that it can fit into the nucleus.

For example, a typical human chromosom e has a DNA strand that could extend to about 6 cm long. This is far too large to fit into a nucleus that is much smaller than the full stop at the end of this sentence.

To enable DNA to fit into a nucleus, it is heavily coiled and folded, very similar to an elastic band twisted repeatedly until it forms a solid ball. Proteins are responsible for holding the DNA in its folded state.

Protein

X Expanded glossary and comprehensive index

DNA

provided for ease of reference

15.2 The structure of a chromosome

Non-coding DNA is DNA that does not cause the production of a protein.

X Suitable for Higher and Ordinary Level students X Student interactive resources and activities are available FREE online at www.edco.ie/biologyplus

X Teachers can access the e-book version of the textbook and a bank of free resources on www.edcodigital.ie

15.1 A variety of chromosomes

Non-coding DNA

Genes are arranged along the DNA of a chromosome in a line. Sometimes a number of genes are located close together on the chromosome. Other genes are widely separated along the chromosome.

This means that large sections of the chromosome are not made up of working genes.

In fact it is known that about 97% of the DNA in a human cell does not consist of genes. This DNA

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is said to be non-coding (i.e. it does not carry the code for the formation of a protein).

The non-coding DNA was often called junk DNA. Recent research indicates that large amounts of this DNA may act as a genetic control panel switching genes on and off.

Non-coding DNA is of two types:

Some of it occurs between genes

Some of it is found within genes.

Genes

Chromosome

Non-coding DNA

15.3 Genes on a chromosome

The Author Michael O’Callaghan, BSc, HDip in Ed, MEd, C Biol, MSB, has almost 40 years’ experience of teaching Leaving Certificate Biology (over 30 of them at St David’s CBS, Artane, Dublin, and he is now teaching at the Institute of Education, Leeson Street). He is the author of numerous Leaving Certificate Biology and Junior Certificate Science textbooks, revision guides, question books and workbooks. For many years Michael corrected Leaving Certificate Biology and Junior Certificate Science examinations.

The Educational Company of Ireland

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Student Revision Website Student interactive resources and activities, including testing, assessment tracking and experiment videos, are available FREE online at www.edco.ie/lcbiologyplus. This interactive website contains a comprehensive set of eLearning materials to aid exam preparation, homework, study and revision and to help test students’ knowledge of the Leaving Certificate Biology course.

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