B2.2: Tissues, organs and organ systems

B2.2.1: Animal Organs

Digestive system


The mouth breaks up food using teeth in a process called mechanical digestion. It contains salivary glands which help to break down carbohydrate by releasing saliva. The saliva contains the carbohydrase called amylase which starts the breakdown of starch into glucose.


This muscular tube carries food from the mouth to the stomach. It pushes food down by a wave of muscular contractions called peristalsis.


In the stomach food is mixed with HCl and enzymes. The stomach wall is protected from the acid by goblet cells that produce mucus which gives the stomach its lining. Food continues to be broken down mechanically by the action of muscles. The enzyme pepsin is present which digests proteins into amino acids.

Gall Bladder

Bile is stored in this organ after being made in the liver. Bile emulsifies fat providing a greater surface area for enzymes to act on. Bile also neutralises the acidic conditions of the duodenum (the area of the small intestine it is connected to).

Small intestine

This is where soluble food molecules are absorbed into the blood by diffusion. The small intestine is adapted to have a good blood supply and a large surface area from lots of tiny villi.


The pancreas produces digestive enzymes in a secretion called pancreatic juice. Enzymes break large molecules into smaller ones that can be more easily diffused through the surface area of the intestine. The enzymes it makes are carbohydrase, protease and lipase.

Large Intestine

Water is absorbed into the blood here. If excess water was not absorbed the faeces would be too runny.


Faeces stored here before excretion


Faeces leave the body through this muscular sphincter

B2.2.2: Plant Organs

Epidermal Tissue – Covers the surface of plants and protects them

Mesophyll Tissue – Contains lots of chloroplasts for photosynthesis

Xylem – a transport tissue which carries water and minerals from the roots to the leaves

Phloem- A transport tissue which carries sugars from the leaves to the rest of the plant

See Book 1

B2.3: Photosynthesis

Carbon Dioxide + water      =>   Glucose + Oxygen

6CO2     + 6H2O     =>   C6H12O6  + 6O2

Limiting Factors

Controlling Plant Growth





B2.4: Organisms and their environment