GCSE Biology Organisation

What are the levels of organisation in a multicellular organism?

Cells → Tissues → Organs → Organ systems → Organism

What is a tissue?

A group of similar cells that work together to carry out a particular function

What is an organ?

A group of different tissues that work together to perform a specific function

What is an organ system?

A group of organs that work together to perform a particular function

What is an enzyme?

A biological catalyst (protein) that speeds up chemical reactions without being used up

What is the lock and key theory of enzyme action?

The substrate fits exactly into the active site of the enzyme (like a key in a lock)

What happens to an enzyme if the temperature is too high?

It denatures – the active site changes shape so the substrate no longer fits

What happens to an enzyme if the pH is too high or too low?

It denatures – the active site changes shape

Name the three main factors that affect enzyme activity

Temperature, pH and substrate concentration

Where is amylase produced and what does it break down?

Produced in the salivary glands and pancreas; breaks down starch into maltose/sugars

Where is protease produced and what does it break down?

Produced in the stomach, pancreas and small intestine; breaks down proteins into amino acids

Where is lipase produced and what does it break down?

Produced in the pancreas and small intestine; breaks down lipids (fats) into fatty acids and glycerol

What is the role of bile in digestion?

Emulsifies fats (breaks large fat droplets into smaller ones) increasing surface area for lipase; also neutralises stomach acid

Where is bile produced and stored?

Produced in the liver and stored in the gall bladder

Name the main organs of the digestive system in order

Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus

What is the function of the stomach in digestion?

Produces protease (pepsin) and hydrochloric acid; churns food into chyme

What is the function of the small intestine?

Main site of digestion and absorption of nutrients

What is the function of the large intestine?

Absorbs water from undigested food and forms faeces

Describe the structure of the human heart

Four chambers: right atrium, right ventricle, left atrium, left ventricle; valves prevent backflow

Why is the left ventricle wall thicker than the right ventricle wall?

It has to pump blood all around the body (higher pressure) whereas the right ventricle only pumps to the lungs

What is double circulation?

Blood passes through the heart twice in one complete circuit of the body (once to the lungs, once to the body)

Name the three types of blood vessel

Arteries, veins and capillaries

What are the main features of arteries?

Thick muscular walls, narrow lumen, carry blood at high pressure away from the heart

What are the main features of veins?

Thinner walls, larger lumen, valves to prevent backflow, carry blood at low pressure towards the heart

What are the main features of capillaries?

Very thin walls (one cell thick) for exchange of substances by diffusion

Name the four main components of blood

Red blood cells, white blood cells, platelets and plasma

What is the function of red blood cells?

Transport oxygen (contain haemoglobin)

What is the function of white blood cells?

Defend against pathogens (phagocytosis, antibodies, antitoxins)

What is the function of platelets?

Help blood clot to prevent blood loss and entry of pathogens

What is the function of plasma?

Transports carbon dioxide, nutrients, hormones, urea and heat around the body