Biology 3 Part 1 Basics- Exchange of Substances

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  • Created by: Rachel
  • Created on: 30-04-08 19:25

B3.1- Diffusion & Active Transport

Active Transport

  • Against the concentration gradient
  • Uses energy from respiration
  • Transport of material through channels in cell membranes

Greater concentration of particles = greater rate of diffusion

Greater concentration gradient = greater rate of diffusion

Diffusion is important for moving substances in and out of cells.

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B3.2- Gas Exchange in the Lungs

LUNGS= located in the thorax, and protected by the ribcage

DIAPHRAGM= sheet of muscle separating the abdomen form the thorax

  • Breath in = diaphragm down, ribs up
  • Breath out = diaphragm up, ribs down

The BRONCHI link the lungs to the TRACHEA.

ALVEOLI= air sacs in the lungs used for gaseous exchange. Adaptions:

  • Big surface area
  • Moist
  • Thin walls- good access to blood stream

The constant breathing of air in/out and the circulation of the blood means there is always a good concentration gradient for diffusion of substances into the blood.

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B3.3- Absorbing Food

Small Intestine - absorbs food molecules

VILLI- create large surface areas (+MICROVILLI), waft through food "soup" and therefore absorb more, 1 cell thick to capillaries- shorter distance for absorption

SMALL MOLECULES GUT--->BLOOD VIA DIFFUSION eg fats, water, mineral ions

OTHER SUBSTANCES GUT--->BLOOD VIA ACTIVE TRANSPORT eg glucose + amino acids. This gives more control over the amounts absorbed.

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B3.4- Absorption in Plants


  • Large, flat, angled to sun to catch as much light as possible
  • Stomata on underside to stop dust blocking them (let gases/water vapour in/out)
  • Air spaces in the leaf used for gaseous exchange


  • Absorb water and dissolved ions
  • Root hair cells- fine, spread into gaps in the soil, creating a greater surface areas and more access to water.
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B3.5- Movement of water through plants

TRANSPIRATION is where water evaporates through the STOMATA in the under side of leaves

This causes a change in the concentration gradient of cells within the plant, causing water to travel up the XYLEM tubes in the plant through osmosis, bringing up vital dissolved ions etc.

WILTING occurs when cells within the plant are not full/rigid with water. When more water is lost through transpiration than gained from the root hair cells, cells can be damaged.

GUARD CELLS can close the stomata, stopping water loss.

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B3.6- Human Blood Circulation

Taking blood:

  • Into heart = veins
  • Out of heart = arteries

CAPILLARIES are very small blood vessels that are found very close to most cells int he body, particularly tissues and organs. They join up to form bigger veins/arteries, and their walls are very thin, allowing easy substance exchange.

Oxygen and glucose go into the cell

Wastes, carbon dioxide, hormones etc go out

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B3.7- Travelling in the Blood

PLASMA= the liquid part of blood. Dissolved substances are transported in this, eg carbon dioxide, hormones the products of digestion and urea.

UREA is formed by the break down of amino acids in the liver. It is transported to the kidneys.

RED BLOOD CELLS= have no nucleus, have a unique shape- this ensures more room to transport oxygen

HAEMOGLOBIN= found in red blood cells. When oxygen is gained, it becomes OXYHAEMOGLOBIN. The red blood cell then transports the oxygen to the body cells, and the HAEMOGLOBIN reverts to DEOXYHAEMOGLOBIN

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B3.8- Exercise and the Body

When you exercise...

  • Heart rate raises
  • Breathing rate raises, and you breathe deeper
  • Arteries dilate in order to supply greater amount of blood
  • Glycogen stores in your muscles and liver transform into glucose for use in respiration

All of these help supply more oxygen to the cells, and get rid of waste CO2, quicker.

Not enough exercise can result in high blood pressure and heart disease.

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