B2 Biology: Cells

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Cell Organelles


Ribosomes: Where Protein Synthesis takes place.

Cell Membrane: Controls the passage of substances in and out of the cell.

Mitochondria: Where energy is released in respiration.

Cytoplasm: Where metabolic reactions controlled by enzymes take place.

Nucleus: Contains chromosomes made of genes, controls activities in the cell.

PLANT CELL ONLY ORGANELLES: All of the above, and...

Cell Wall: Strengthens the cell.

Chloroplasts: Absorb light to make food.

Vacuole: Filled with cell sap.

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Microbial Cells

-Yeast is a single-celled fungus, and it has cell walls but they are not made of cellulose like normal plant cell walls. Fungi cannot photosynthesise because they haven't got any chloroplasts. 

-Algae have similiar cells to plant cells.

-Bacteria do not have a nucleus, and their genes are in the cytoplasm.

-Viruses are not made of cells, and they don't have cell membranes, cytoplasm or a nucleus. Most of them are made of a sphere of protein, with some DNA inside it, and they are a hundred times smaller than a cell.

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Cells and Diffusion

What is diffusion?

Diffusion is the spreading of the particles of a gas, or of any substance in solution, resulting in a net movement from a region where they are of a higher concentration into a region where they are of lower concentration. 

Most cells need oxygen so they can respire; oxygen can diffuse into cells.

-Visking tubes contain millions of tiny holes which only let small molecules, like water, diffuse through. Large molecules, such as starch, cannot cross the membrane-it is partially permeable. This is similar to a cell membrane, so visking tubes can be used as a model of a cell.

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Specialised Cells

The body contains hundreds of different kinds of specialised cells.

Red blood cells: Transport oxygen from the lungs to body tissues for aerobic respiration. 
ADAPTED BECAUSE: They contain haemoglobin, an iron pigment that carries oxygen / Do not contain a nucleus, increases volume / Very flexible so they can move through narrow blood vessels.

Ciliated cell: Push and move mucus from one place to another.
ADAPTED BECAUSE: Has a thin layer of moving hairs called cilia.

Goblet cell: Found in the lining of the alimentary canal, and make mucus which helps food slide easily.
ADAPTED BECAUSE: Helps stop bacteria getting down into your lungs. 

Root hair cell: Fine, hair-like extensions of a root.
ADAPTED BECAUSE: Their large surface area enables plants to maximise their absorption of water from the soil.

Sperm cell: Fertilises a female egg cell.
ADAPTED BECAUSE: Tail to propel, mitochondria for energy.

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Structure and function of tissues

The cells that make up tissues are adapted for particular roles. 

-Muscular tissue is specialised to produce movement.

-Glandular tissue is made up of cells that secrete useful substances such as hormones or enzymes. 

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Single-celled and multicellular organisms

Multicellular organisms have many different cells which are specialised for a particular function, an advantage over single celled organisms.

Some processes are easier for single celled organisms. Oxygen can easily diffuse into a single cell.

Multicellular organisms need a transport system to bring oxygen to every cell in their body. They also have specialised tissue that are adapted for allowing things to move in and out of the body quickly.

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