3 The Structure of Animal Cells

Key Idea: Animal cells are eukaryotic cells. They have features in common with plant cells, but they also have several unique features.

The structure of a relatively unspecialised animal cell (a liver cell)

Mitochondria

Oval-shaped organelles bounded by a double membrane.

Smooth endoplasmic reticulum (smooth ER)

An interconnected network of membranes. A site for lipid and carbohydrate metabolism, including hormone synthesis.

Rough endoplasmic reticulum (rough ER)

is ER an interconnected network of membrane with ribosomes attached to its surface. Proteins destined for transport outside of the cell are made here.

Ribosomes

These manufacture proteins. They may be free in the cytoplasm or associated with the surface of the endoplasmic reticulum.

Golgi apparatus

A series of flattened, disc-shaped sacs, stacked one on top of the other and connected with the ER. The Golgi stores, modifies, and packages proteins. It ‘tags’ proteins so that they go to their correct destination.

Microvilli

Small projections which increase the surface area for absorption (not all animal cells have these).

n

Cytoplasm

A watery solution containing dissolved substances, enzymes, and the cell organelles and structures.

Lysosome

These contain enzymes that break down foreign material.

Plasma membrane

Phospholipid bilayer with associated proteins and lipids. Controls the movement of substances in and out of the cell.

Nuclear pore

A hole in the nuclear membrane. It allows communication between the nucleus and the rest of the cell.

Nucleus

A large organelle containing most of the cell’s DNA. Within the nucleus, is the nucleolus (n). It is involved in ribosome synthesis.

Centrioles

Microtubular structures associated with nuclear division.

3D

Features of an animal cell

Animal cells are eukaryotic cells. Features that identify animal cells as eukaryotic cells include: fPresence of a membrane-bound nucleus. fPresence of membrane-bound organelles (e.g. mitochondria, Golgi apparatus, endoplasmic reticulum, lysosomes). Animal cells share many of the same structures and organelles that plant cells have, but they also have several features not seen in plant cells. Features which can be used to identify an animal cell include: ` Centrioles ` Irregular shape ` Lack of a cell wall ` Lack of chloroplasts

Many animal cells are specialised to carry out specific functions within the body. As a result, the morphology and physiology of animal cells are highly varied. Some examples are presented here.

A

Neurones (nerve cells) in the spinal cord

B

C Nerve cell

1. The two photomicrographs (left) show several types of animal cells.

Identify the features indicated by the letters A-C:

A:

B:

C:

2. White blood cells are mobile, phagocytic cells, whereas red blood cells are smaller than white blood cells and, in humans, lack a nucleus.

(a) In the photomicrograph (below, left), circle a white blood cell and a red blood cell:

(b) With respect to the features that you can see, explain how you made your decision.

3. Name and describe a structure or organelle present in generalised animal cells but absent from plant cells:

4. Briefly describe the function of the following:

(a) Microvilli:

(b) Ribosomes:

(c) Golgi apparatus:

(d) Rough endoplasmic reticulum (rER):

White and red blood cells (blood smear)

Photos: EII