Biology B3 Revision Notes

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  • Created by: RATM33
  • Created on: 10-01-10 16:04

Diffusion and Osmosis


  • The net movement of substances from an area of high concentration to an area of low concentration
  • Is passive - no energy is required
  • The greater the temperature, the greater the rate of diffusion
  • The steeper the concentration gradient, the greater the rate of diffusion


  • The movement of water particles across a partially permeable membrane from an area of high concentration to an area of low concentration
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Active Transport

Active Transport

  • Goes against the concentration gradient - (from an area of low concentration to and area of high concentration)
  • Uses energy from respiration - (is active)
  • uses ATP
  • Aided by protein carrier molecules
  • enables cells to absorb ions from dilute solutions
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Uses of Active Transport

In Root Hair Cell

  • There is a greater concentration of minerals in the cell rather than in the soil surrounding
  • If diffusion were to take place, minerals would move out of the plant
  • To absorb all nutrients, active transport is required

In the Gut

  • During digestion, there is sometimes a higher concentration of glucose and ammino acids in the blood, rather than in the gut
  • If diffusion were to take place, the glucose and amino acids would move out of the blood
  • To absorb all glucose and amino acids, active transport is required.
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The Lungs

The lungs are...

  • In the throax (upper part of the body)
  • protected by the ribcage
  • separated from the abdomen (lower part of the body) by the diaphragm

The Breathing system:

  • Takes air into and out of the body
  • So that Oxygen can diffuse into the bloodstream
  • Carbon Dioxide can diffuse out of the bloodstream, into the air
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Air travels from the -

Trachea --> Bronchus --> Bronchiole --> Alveoli

Breathing In -

  • Intercorsal muscles and diaphragm contract
  • Thorax volume increases
  • Decreases pressure, drawing air in

Breathing Out -

  • Intercorsal muscles and diaphragm relax
  • Thorax volume decreases
  • Air is forced out
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Gas Exchange

  • Occurs in the alveoli
  • Oxygen diffuses into the blood
  • Carbon Dioxide diffuses out of the blood, and breathed out

The Alveoli are specialised to maximise diffusion, they have -

  • A large surface area
  • Moist lining (so gases can diffuse easily)
  • Thin walls (short diffusion distance)
  • Rich blood supply
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  • Found on the lining of the small intestine
  • Aid in digestion
  • Digested food moves in through diffusion and active transport

The Villi are adapted for digestion -

  • Large surface area
  • Thin walls (short diffusion distance)
  • Rich blood supply (assists quick absorption)
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Gas Exhange in Fish (1)

Are large and move alot, so therefore have breathing systems

Gills (a diagram would be useful to understand this, the link to it is in the overview bar)

  • groups of blood vessels in a thin membrane bag
  • absorb oxygen dissolved in water
  • protected by operculum (gill cover)
  • arranged in 4 layers on each side
  • supported by gill arches
  • in the form of filaments, which provides a large surface area
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Gas Exhange in Fish (2)

Lamellae - respiratory surface for fish

  • Thin Walls
  • Branched (surface area)
  • Good blood supply
  • Counter current against blood supply
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Gas Exchange in Insects

Are small and do not move alot, and therefore have small breathing systems or a blood supply

  • Have holes on their body surface called spiracles, where air enters
  • These lead to thracheae (small tubes)
  • which branch off to tracheoles
  • gases diffuse out of here and into cells

Air --> Spiracles --> thracheae --> tracheoles --> cells

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Gas Exchange in Plants

Leaves are the surface for gas exchange in plants

They are adapted to this because -

  • Thin (decreases distance for diffusion)
  • Flattened shape - increase surface area
  • Internal air spaces (increases the opportunity for gas exchange)

They have stomata to obtain carbon dioxide from the atmosphere

These are pores which allow CO2 in and O2out

The size of the stomata is controlled by the guard cells

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Water Maintainence in Plants

Plants lose water vapour from the surface of their leaves

Transpiration - the loss of water vapour from the surface of a leaf through evapouration

Most transpiration is through the stomata

The transpiration stream is a constant movement of water molecules

Wilting is a protection mechanism against further water loss - the leaves collapse and hung down, which means that the surface area for water loss is reduced

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Factors that affect Transpiration

LIGHT - as light intensity increases, stomata open wide (to allow more CO2 for gas exchange), which increases the rate of transpiration

HUMIDITY - Diffusion - greater concentration on outside, rate of transpiration slows

TEMPERATURE - More water molecules evapourate, rate of transpiration increases

WIND - water evapourates quicker, molecules dissolved are carried away

WATER SUPPLY - Plants close stomata when water levels in the soil are low, rate of transpiration decreases

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Circulatory System in Humans

The heart pumps blood around the body

Blood flows from the heart to the organs through arteries and returns through veins

Substances needed by the cells in the body tissues pass out of the blood

Substances produced by the cells into the blood through the walls of the capillaries

There are two separate circulation systems (double circulatory system); one to the lungs (deoxygenated blood) and one to all the other organs of the body (deoxygenated)

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The Blood

Blood Plasma transports:

  • Carbon Dioxide - organs --> lungs
  • Soluble products of digestion - from small intestine -> organs
  • Urea - from the liver --> kidneys

Red Blood Cells:

  • Transport oxygen - from lungs --> organs
  • Have no nucleus - more space for oxygen
  • Contain haemoglobin - contains iron
  • in the presence of haemoglobin forms oxyhaemoglobin
  • in other organs it splits up into oxygen and haemoglobin (deoxyhaemoglobin)
  • Biconcave Disc shape - surface area + easy to fit in capillaries
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Effect of exercise on the body

The energy that is released during respiration is used to enable muscles to contract

During exercise -

  • Heart rate increases - increase blood flow, so amount of oxygen and glucose that is transported to the lungs increases and amount of carbon dioxide removed increases
  • Rate and depth of breathing increases - to increase amount of oxygen taken in and carbon dioxide released
  • Arteries supplying muscles dilate (vasodilation) - to increase blood flow
  • Glycogen stores in muscles and liver transformed into glucose for use in respiration
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Anareobic Respiration

If muscles are subjected to long periods of vigorous activity, they become fatigued (stop contracting efficiently)

If insufficient oxygen is reaching the muscles, they use anaerobic respiration to obtain energy.

Anaerobic respiration is the incomplete breakdown of glucose, and therefore releases less energy compared to Aerobic respiration

C6H12O6 --> 2C3H6O3 + 2 ATP

Glucose --> Lactic Acid + Energy

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Anaerobic respiration results in an oxygen debt that has to be repaid in order to oxidise lactic acid into carbon dioxide and water.

Lactic Acid --> Carbon Dioxide + Water

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The Kidneys

We have2 kidneys in our body

The Kidneys:

  • Prevent the build up of toxins in the blood
  • Control the levels of water in the blood (Osmo regulation)
  • Control the concentration of ions in the blood (Ion-regulation)
  • Produce urine - (a mixture of water, ions and urea)

A build up of excess protein can cause a build up of ammonia in the body, which is poisonous.

The protien is sent to the liver, where it is broken down into - glucose and UREA. The urea is sent to the kidneys.

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Ultrafilteration, Reabsorption and Excretion

A healthy kidney produces urine by (see diagram) -

  • Filtering blood (ultrafiltration) - high pressure builds up in the bundle of blood capillaries, the membranes between the capillaries and the Bowman's capsule act like a filter and filter out glucose, ions and water. The red blood cells and protein are too large to fit in the filter so they remain in the blood.
  • Reabsorbing ALL glucose - through active transport
  • Reabsorbing sufficient ions
  • Reabsorbing suffcient water
  • Releasing urea, ions and water as urine
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Kidney Failure

If the kidneys do not work properly, waste substances can build up in the blood, which can result in death.

There are two ways in which Kidney failure can be treated:

  • Kidney Dialysis
  • Kidney Transplant
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Kidney Dialysis

During Dialysis -

  • Blood from an artery
  • flows through a dialyser (machine)
  • the dialysis fluid contains the same concentration of glucose as the blood
  • contains ions and water at optimum conditions
  • there is NO urea in the dialysis fluid and a greater concentration in the blood, so there is a steep concentration gradient
  • the blood flows through a partially permeable membrane
  • flows at a counter current
  • "Clean" blood flows back into the body through a vein
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Kidney Transplant

A kidney transplant enables a diseased kidney to be replaced with a healthy one from a donor.

The healthy kidney is attached to the bladder with a transplanted ureter (diagram)

As with all transplants, there is a high risk of the kidney getting rejected by the body.

This can be prevented by -

  • getting a donor kidney with a tissue type similar to that of the patient
  • treating the patient with immunosuppressant drugs
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Advantages and Disadvantages of Transplants over D


  • No build up of toxins/ keeps blood concentration levels consant
  • Prevents high blood pressure
  • No restricted diet
  • No Time wasted on dialysis
  • Risk of infections from dialysis
  • Risk of blood clots from dialysis
  • Transplants are cheaper than dialysis


  • Rejection
  • Use of Immunosupressant drugs
  • Dangers during operation
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The theory of biogenesis states that -


The theory of spontaneous generation or abiogenesis states -


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Theodor Schwaan

  • His method was to expose boiled broth only to heated air in a glass tube
  • The result being that no micro-organisms were detectable
  • He was convinced that the idea of spontaneous generation was false
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Lazzaro Spallanzani

  • Believed in biogenesis
  • Knew that boiling killed microbes

His experiment -

  • Boiled 2 sets of broth to kill microbes
  • Sealed one flask, and left the other one open in air
  • Only one went off
  • This showed microbes got into food from air


Some said that it only proved that spontaneous generation occurs in air

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Louis Pasteur

  • Heated broth in 2 flasks, both open in air
  • one has a swan neck so the microbes settle in the bend
  • The broth in the swan neck stayed fresh
  • The broth is the open neck didn't

This concluded that there was no "life force" in the air, and disproved spontaneous generation

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Food Production - Cheese

Cheese is made using BACTERIA

  • Bacteria added to milk
  • Produce solid curds
  • Curds separated from whey
  • Enzymes can be added to speed up separation
  • Add more bacteria
  • Leave to ripen
  • Mould/ Bacteria added to give flavour
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Thanks for this brilliant resorse :)

Nadeem P - you wont get anywhere coppying :/


hey, do we need to know about fish??? :)


not really, i doubt they'll ask you about it, but its basically the same thing, like bigger surface area etc...



This Helped Me Soo Much

Thank Yhuu !!!



Heather Greetham

THIS IS AMAZING! thank you so much! i have a resit soon, and this is going to help immensely! :P




Thank You!


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