Biology (B2) - Cells and Cell Structure

This set is for B3 Biology, AQA, and specifies with Cells and Cell Structure using Nigel English as guide. This topic has five subtopics which are:

Animal Building Blocks          Plant and Alga Building Blocks          Bacteria and Yeast Cells          Getting In and Out of Cells          Specialised Organ Systems

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Animal Building Blocks

Every cell has a cell membrane that holds  the cell together and controls what goes in and out of the cell.

Inside the cell there are organelles which have a specific job, the nucleas controls the cell's activities and is surround by watery cytoplasm, it controls the DNA which provides the instructions for synthesising the chemicals the cell needs, like enzymes.

Mitochondria perform respiration. 

Ribosomes are the smallest organelles. They build up or synthesise proteins from amino acids. These proteins make enzymes. 

Many cells are specialised for specific tasks, muscle cells are full of mitochondria for photosynthesis.

Sperm cells have tails that help them for swimming to go to the egg and also have a high amount of mitochondria to get energy for moevement.

Nerve cells have long fibres carrying electrical impulses.

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Plant and Alga Building Blocks

As well as a nucleas, mitochondria, ribosomes and a cytoplasm, plant cells also have cell walls made of a carbohydrate called cellulose. This cellulose in the wall is in the form of fibres making a strong pack supporting the cell. 

Some plant cells also have chloroplasts containing chlorophyll which capture sunlight to then use for photosynthesis. 

Many plant cells also have a vacuole which has a liquid called cell sap containing sugars, salt and water. It makes the cell firm when full. 

Plants also have specialised cells. Palisade mesophyll cells are found in the leaf and are full of chloroplasts as they are the main photosynthetic cells.

Root hair cells have a large surface area to absorb lots of water and dissolved mineral ions. They are also small to fit through gaps in the soil.

Xylem vessels are dead empty cells but has chemicals so it doesn't rot away. It is arranged as a tube of only a cell wall so water can be transported from the roots to the leaves.

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Bacteria and Yeast Cells


Bacteria are unicellular organism meaning it is made up of one cell.

A bacteria cell have a cell membrane, a soft cell wall and a cytoplasm around a circular chromosome of DNA and plasmids which are just small circles of DNA.


Natural yeast can be found on the surface of fruits, a plant's leaf and flower, soil, dust, water, milk and even on the surface of our body. 

A yeast cell has a cytoplasm, a vacuole, mitochondrion, a cell membrane, a cell wall and a nucleas.

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Getting In and Out of Cells

Particles can move through the air through diffusion as they go from a high to low concentration. 

When a soluble substanc is put in water the particles move in all different directions and bump into one another, by doing this they spread out slowly. This happens until they are evenly spread in the water.

A difference of concerntrations in two areas is known as a conentration gradient.

Substances move in and out of cells exactly like this. They move through the cell membrane. Overall net movement is from a high to low concentration gradient across a semi-permeable membrane. We say 'semi' as large particles cannot go through.

Oxygen is a good example as they move from the alveolus in the lungs to the red blood cells. From the red blood cells they then go into other body cells that need oxygen for respiration.

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Specialised Organ Systems

In multi-cellular organisms, the same specialised cells form a tissue. 

For example, animals have epithelial cells that make a tissue which covers the linings inside the body, and muscle cells also make a muscle tissue. A plant also has many specialised tissue in the leaf like mesophyll tissue and epidermal tissue.

Groups of different tissues make up an organ. For example, a stomach has three layers of muscular tissue, the inner wallhas glandular tissue and epithelial tissue lines the outside. 

Several different organs make up an organ system. For example, the digestive system contains the salivary gland, the stomach, the pancreas and the small and large intestine all for the breaking down of food.

Plants also have organs, one is a leaf with the specific function to absorb light for photosynthesis. Another is the root designed to absorb water and minerals. The last one is the stem which holds the leaves at a good position to absorb sunlight. 

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