Biology B3 2.1-2.7

UNIT 3 Biology

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The Circulatory System

3 elements : blood vessel, heart and the blood

Humans have a double circulation which is important for warm-blooded mammals

Fully oxygenated blood returns to the heart from the lungs and can be sent around the body.

Blood Vessels:

1. ARTERY- carries blood away from the heart to organs.

2. VEINS- carries blood to the heart, is low in oxygen and has valves to prevent backflow of the blood.

3. CAPILLARY- are narrown and have thin walls which allow oxygen and glucose to pass through them easily (from the bloos into cells) by diffusion

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The heart is made of 2 pumps and its walls are almost entirely muscle.


  • PULMONARY ARTERY- takes deoxygenated blood to the lungs
  • PULMONARY VEIN- brings oxygenated blood from the lungs
  • AORTA- carries oxygenated blood around the body
  • VENA CAVA- brings deoxygenated blood into the heart
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Transport in the Blood

The liquid part of the blood is called the PLASMA.

blood contains:



- yellow liquid

- transports all your blood cells

-CO2 produced in the organs is carried in the plasma back to the lungs

- small and soluble products of digestion pass into the blood from the gut and are then carried around the body in the plasma to organs and cells.

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- pick up oxygen from the lungs and carry it to the tissues and cells.

- bioconcave disc shape, increases the SURFACE AREA:VOLUME ratio.

- contains haemoglobin (which carries oxygen)

- has no nucleus which leaves more space for haemoglobin molecules.

PLATELETS - clot the blood at the sight of a wound

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Haemoglobin is a large protein molecule folded around 4 iron atoms

Haemoglobin reacts with oxygen to form oxyhaemoglobin

-Lungs have a high oxygen concentration

- Cells have a low oxygen concentration therefore oxyhaemoglobin splits back into haemoglobin and oxygen. The oxygen then diffuses into the cell.

People who do not have enough iron in their bodies suffer from anemia which makes their skin pale and they become weaker.

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Substances are TRASNPORTED around your body in your BLOOD.

Disolved molecules such as GLUCOSE and waste substances such as UREA are carried in the PLASMA while OXYGEN is carried from the LUNGS to the cells by your RED BLOOD CELLS.

Blood PLASMA trasnports food molecules, urea and carbon dioxide.

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The Effect of Exercise on the Body

Muscles use a lot of energy.

Muscle tissue is made up of protein fibres which contract when they are given energy from respiration.

Muscles contain GLYCOGEN stores which is a carbohydrate that can be broken down into GLUCOSE.

glucose+oxygen---> carbon dioxide+water+energy

Aerobic Respiration is the process by which food molecules are broken down using oxygen to release energy for the cells.


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When you exercise your muscles contract harder and quicker.

They need more glucose and oxygen to supply their energy needs.

Muscles also produce a lot of carbon dioxide which constantly needs to be removed.


- Heart rate increases and arteries supplying blood to muscles DILATE. This increases blood flow to the muscles which is carrying glucose and oxygen at a faster rate. (increases the removal of CO2)

- breathing rate increases and you breathe more deeply. You breathe more often and bring more air into the lungs. Increase of oxygen brought into the body and carried to muscles by red blood cells.


  • increases the size of the lungs and heart
  • develop a bigger and more efficient blood supply
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Anaerobic Respiration

Muscle Fatigue- STOP contracting efficiently, short of oxygen.

in anaerobic respiration glucose molecules are not broken down completely.


Glucose--->lactic acid+energy

OXYGEN DEBTis the amount of oxygen needed to break down the lactic acid.

oxygen debt repayment is

lactic acid+oxygen--->carbon dioxide and water

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