Biology - Unit B2

Revision cards for unit B2 of the biology course, it involves the topics;

- Cells and Simple Cell Transport (B2.1)

- Tissues Organs and Organ Systems (B2.2)

- Photosynthesis (B2.3)

- Proteins - Their Function and Uses (B2.5)

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Animal Cell - small vacuole (contains material being taken in or removed by cell), mitochondria (power station of cell), cell membrane (controls entry and exit of chemicals - selectively permeable barrier), nucleus (controls all cell's functions - contains DNA in chromosomes), cytoplasm (solution of numerous chemicals dissolved in water)

Plant Cell - nucleus, cytoplasm, mitochondria, vacuole membrane (controls exchange of chemicals between vacuole and cytoplasm - selectively permeable), chloroplast (contains chlorophyll - site of photosynthesis), large (sap) vacuole (contains water and few dissolved chemicals, provides support), cell wall (provides support, made of strong cellulose fibres), cell membrane (selectively permeable barrier to chemicals)

Differentiation - cells also become specialised to do a particular job, this is called differentiation.

Bacterial Cells - ribosomes (make proteins), DNA, cell membrane, cell wall (murein), cytoplasm (cell reactions occur), slime capsule (protects cell), flagellum (tail) A lot smaller than animal and plant cells, no nucleus.

Fungal Cells - vacuole (possibly), nucleus, cell membrane, cell wall - not cellulose (chitin), mitochondria, cytoplasm - Yeasts reproduce asexually by producing buds. 

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Tissues, Organs and Organ Systems

A tissue is a group of similar cells which work together.

Organs - tissues group together to from organs. Organs are usually made up of several types of tissue.

Organ system - a group of organs working together e.g. endocrine system, nervous system, respiratory, reproductive.

Salivary glands - make salva to help food go down your throat and digest sugar

Pancreas - contains carbohydrates, enzymes digest food

Stomach - churns up food and digests proteins

Small intestine - absorbs nutrients and minerals from food into the blood

Liver - aids digestion, extracts nutrients, breaks down harmful substances

Large intestine - absorbs water and removes useless waste from body

Plant organs - flower (petal, stamen, carpel - used for reproduction), leaf (produces food by photosynthesis), stem (supports plant and transports substances through plant), roots (anchors plant and takes up water and minerals from soil). 

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Photosynthesis is a chemical reaction. Carbon dioxide and water react with the help of light and chlorophyll, the reactants are converted into glucose and oxygen.

Carbon dioxide + water à glucose + oxygen

6 CO2 + 6 H2O à C6H12O6 + 6 O2

Epidermis - protection, transparent to let light through

Spongy mesophyl cells - gases diffuse (large air spaces)

Stomata - tiny holes allow gases in and out

Guard cells - two surround each stoma

Veins - made of xylem (gives stength, supports plant, hollow to transport water) and phloem (hollow allows sugars to move through plants - neighbouring cells supply energy)

Palisade cells - closely packed, lot of chloroplasts (photosynthesis)

Waxy cuticle - prevents water loss by evaporation

Rate of photosynthesis varies depending on the amount of - light, carbon dioxide and the temperature

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Proteins - part 1


  • needed in the diet for growth and repair
  • structure - muscle, collagen in skin, tendons, ligaments and keratin in nails and hair
  • antibodies - defence against disease
  • haemoglobin - transport of oxygen in blood
  • hormones - insulin, growth hormone, FSH
  • enzymes - amylase, lipase, catalyse

Proteins are made up of long chains of amino acids joined together. They are folded to produce a specific 3D shape. Different properties will have their own unique shape.

Enzymes - biological catalysts made of protein.

Catalysts - they speed up chemical reactions without being charged.

Enzymes are specific. They will only catalyse one particular reaction.Different enzymes work best at different pH values. Some enzymes work outside the body cells. Digestive enzymes - produced by specialised cells in glands and lining of the gut. Enzyme, amylase - produced in salivary gland, pancreas and small intestine. It breaks down starch into sugars in mouth and small intestine. Protease enzyme - produced in stomach, pancreas and small intestine, break down proteins into amino acids in stomach and small intestine. 

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Proteins - part 2

Lipase enzyme - produced by pancreas and small intestine, break down lipids (fats and oils) into fatty acids and glycerol in small intestine. Stomach produces hydrochloric acid, enzymes in the stomach work most effectively in these acidic conditions. 

Liver produces bile - stored in gall bladder before released into the small intestine. Bile neutralises the acid in the stomach, it provides alkaline conditions which the enzymes in small intestine work most effectively.

Some microorganisms produce enzymes that pass out of the cells. These enzymes have many uses in the home and in industry:


  • biological detergents contain protein-digesting + fat digesting enzymes (proteases+lipases)
  • biological detergents are more effective at low temperatures than other types of detergents.


  • proteases are used to 'pre-digest' the protein in some baby foods
  • carbohydrases are used to convert starch into sugar syrup
  • isomerase is used to convert glucose syrup into fructose syrup - much sweeter and therefore can be used in smaller quantities in slimming foods.

Most enzymes are denatures at high temperatures and many are costly to produce.

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