Cell Structure

A typical animal cell

• - All cells have structures inside them - these are called sub-cellular structures.
• - In an animal cell, the sub-cellular structures include:
• - nucleus, which controls the activities of the cell and contains the genetic material.
• - cytoplasm, in which most of the chemical reactions take place.
• - a cell membrane, which controls the passage of substances in and out of the cell.
• - mitochondria, where areobic reputation takes place.
• - ribosomes, where proteins are made.

Plant cells

• - Plant cells and algal cells conatin all the sub-cellular structures found in animal cells.
• - They also have:
• - a cell wall, made of cellulose, which strengthens the cell.
• - a permanent vacuole, that is filled with cell sap, which supports the plant.
• - Plants need to make their own food, so some of their cells contain chloroplasts.
• - Chloroplasts absorb light to make food (glucose) through photosynthesis.

Prokaryotic and Eukaryotic cells

• - There are two main types of cell:
• - Prokaryotic
• - Eukaryotic
• - Plant, animal and fungal cells are all eukaryotic.
• - Bacterial cells are prokaryotic.
• - Prokaryotic cells are much smaller in size and:
• - the genetic material is not enclosed in a nucleus.
• - the genetic material is a single DNA loop and there may be one or more small rings of DNA, called plasmids.
• - they do not contain mitochondria or chloroplasts.

A typical bacteria cell

• - Bacterial cells have many different shapes - some are round, some are rod-shaped and some are spiral - but they are all prokaryotic cells.
• - In bacterial cells, the roles of mitochondria and chloroplasts are taken over by the cytoplasm.
• - There may be one or more flagella, which are tail-like structures that move the bacterium.
• - Plasmids are present, which are loops of DNA that can be transferred from one cell to another.
• - Plasmids allow bacterial cells to move genes from one cell to another.

Key points

• Not all plant cells have chloroplasts. For example, they are not present in root cells because those cells do not receive any light.
• Prokaryotic cells are much more simpler in structure than eukaryotic cells.

Key point

• Plasmids have become very useful to scientists. They allow genes to be inserted into bacteria in genetic engineering.

Key words

• - sub-cellular structures
• - nucleus
• - cytoplasm
• - cell membrane
• - mitochondria
• - ribosome
• - cell wall
• - cellulose
• - vacuole
• - chloroplast
• - prokaryotic
• - eukaryotic
• - plasmid
• - flagella