Biology B7

OCR 21st Centurt Science, GCSE Biology B7 topics

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  • Created by: chloe
  • Created on: 07-06-11 18:06

B7.1 Living organisms are independent

Why do we need the Sun?

The Sun provides:

  • Thermal enegry - helps keeps Earth's atmosphere warm
  • Light energy - green plants use to make food chemicals

- Animal, fungi and bacteria depend Directly/Indirectly on plants for food. So life on Earth is dependant on the Sun's energy.

How do plants harness the Sun's energy?

- Only green parts aborb light  energy. they use it to make food in photosynthesis. Plants absorb a tiny amount of the Sun's energy.

- New material made by photosynthesis consists of chemicals such as carbohydrates, fats and proteins. these form new plant cells and any food stores inside those cells.

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B7.1 Living organisms are independent

Do all organisms in the ecosystem feed in the same way?

- Organisims that make their own food are autotrophs. Most are green plants. A few non green microorganisms are also autotrophs. They dont use light to make their food.

- Organisms that can't make their own food are heterotrophs. These include animals, bacteria and fungi. They depend on the food produced by autotrophs.

                If heterotrophs feed on:                                               We call them: 

  •  Plants................................................................................... Herbivores
  • Animals that have eaten plants............................................. Carnivores
  • Waste produced by plants and animals................................ Decomposers
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B7.1 Living organisms are independent

How are food and energy transferred between organisms in the ecosystem?

- When an animal eats a plant, the energy stored in the plant is transferred to the animal. The chemicals in watse material and dead plants and animals are also an energy store. This energy is transferred to the decomposers that feed on them.

- We can show what eats what by using food chains. Food chains also show the direction of energy transfer:

autotroph----------> heterotrophs

producer-----> primary consumer-----> secondary consumer-----> tertiary consumer

                                     ^-------------------------------trophic (feeding) level-------------------------------^

     food chain:                       grass-----> snail-----> blackbird-----> kestrel

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B7.1 Living organisms are independent


- A pyramid of numbers shows the number of organisms at each feeding level in an ecosystem. It gives you no idea of the biomass at each level.

- A pyramid of biomass shows the number of organisms at each feeding level. So it shows how much food is available at the next level.

- A pyramid of biomass is bigger at the base than at the top because some of the mass does not pass on to the next level. If lots of smaller organisms feed on a few large ones in an ecosystem, a pyramid of numbers isn't a pyramid shape.


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B7.1 Living organisms are independent

How is energy lost from food chains?

- There is less biomass at each level in a food chain. So there is less energy. the energy not passed on is:

  • in uneaten parts
  • used for life prcesses such as movement and keeping warm
  • lost to the surroundings as heat energy
  • in waste products

- Because there is less food and energy at each level, there is a limit to the length of food chains. To calculate the paercentage efficiency of energy transfer at different stages of the food chain:


If 2 units of energy out of 20 are transferred, the percentage transferred is :2/20 x 100 = 10%

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B7.1 Living organisms are independent

What is in soil?

Soil contains:

  • biomass. That includes the living organisms and decaying materials
  • inorganic particles such as sand, silt and clay
  • air
  • water dissolved with mineral ions

To calculate the percentage of water:

  • mass of soil at start = 50g
  • mass of soil when dried to constant mass = 35g
  • loss of mass (or water lost) = 15g
  • %loss = 15/30 x 100 = 30%
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B7.2 Photosynthesis

What happens during photosynthesis?


6CO2 + 6H2O --------------------------->  C6H12O6 + 6O2


Carbon dioxide + Water  --------------> Glucose + Oxygen

  • The green chemical chlorophyll absorbs light
  • The energy is used to rearrange the atoms of carbon dioxide and water
  • The products are glucose ( a sugar) and oxygen ( a waste product)
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B7.2 Photosynthesis

How do plants use the glucose?

  • convert some of the glucose into chemicals needed for growth of plant cells, such as cellulose, protein and chlorophyll.
  • covert some into starch for storage
  • use some in respiration to release energy

Because starch is insoluble, it has little effect on the osmotic balance of cells. A high concentration of glucose causes water to be drawn into the cell. so starch is a better storage molecule than glucose.

Energy released in respiration is used to synthesise polymers such as:

  • starch and cellulose from glucose
  • amino acids and then proteins from glucose and nitrates

Plant roots absorb nitrates by active transport, a process which needs energy.


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B7.2 Photosynthesis

Why does photosynthesis vary?

The rate of photosynthesis may be limited by low:

  • temperatures
  • carbon dioxide concentration
  • light intensity

The amounts of carbon dioxide and oxygen exchanged over a 24 hour period vary. at compensation points, the rate of photosynthesis and respiration balance, so there is no net movement of these gases between a plant surrounding atmosphere.

The rate of photosynthesis is limited by the factor that is in shortest supply.

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B7.3 Heterotrophic nutrition

Recognising different asscociations of organims

- Corals and the green algae in there cells benefit eachother, so they have a symbiotic relationship.


- An orchid attatched to a tree does no harm to the tree, but the orchid benefits by getting more light. this is commensalism.


- Parasitism is close association between 2 organisms of different species, which only benefits the parasite and is harmful to the host. E.G. tapeworms and the maleria parasite.


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B7.3 Heterotrophic nutrition

How do parasites survive?

- Parasites have to be adapted to finding their host, and for living in/on host. The eveolution of a parasite is closely linked to it's host.


  • have suckers and/or hooksto grip to th gut wall
  • have a thick cuticle to resist enzymes
  • can respire anaerobically, they can manage without oxygen
  • have both male and female sex organs, so reproduce without a mate
  • produce lots of eggs to increase the chances of eggs finding a new host

Maleria parasites:

  • are spread to new hosts by mosquitoes
  • live inside red blood cells when in blood; protected from immune system
  • have different surface markers at different stages of life cycle; not recognised by white blood cell.
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B7.3 Heterotrophic nutrition

Parasites cause problems such as:

  • human diseases, including maleria
  • reduced food yeilds (both plants and animals)

Sickle cell anemia, caused by a faulty recessive allele that codes for haemoglobin. Some red blood cells go out of shape causing these symptoms:

  • severe pain, when sickled red blood cells block tiny blood vessels
  • anemia as damaged cells cant be replaced fast enough
  • tiredness caused by shortage of oxygen

- However people who carry one sickle-cell allele are less likely to get malaria. They have an improved chance of survival. So, the freqeuncy of the sickle-cell allele has increased where malaria is a problem. This is natural selection.

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B7.4 New technologies

What is the structure of babcteria?



What can we make using microorganisms?

We can grow bacteria and fungi on a large scale in fermenters using fermention.

Products made this way include:

  • Antibiotics
  • single cell protein; microbes grown for food
  • enzymes for food manufacture, e.g rennin for making cheese

Some of these are made using genetically modified microorganisms.

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B7.4 New technologies

How are cells genetically modified?

When scientists genectically modify an organism, they alter or modify its characteristics by transferring genes from another organism into its DNA.


Find the gene that they want to transfer from one species to another -----> cut it our using enzymes ----->make lots of copies of the gene ------> the transfer the copies to cells of the other species.

 N.B. They use a vector (carrier), a virus or a plasmid, to transfer the genes. Some examples of genetic modification are:

  • modifying microorganisms for making - Drugs such as improved froms of anitibiotics, - hormaones as an insulin.
  • modifying crop plants to make them resistant to pests and diseases.

You need to discuss the ecomnomic, social and ethical implications for the release of genectically modified organisms into the enviroment.

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B7.4 New technologies

How can we use DNA technology in genetic testing?

Scientists can use genetic testing to identify faulty alleles in:

  • adults
  • fetuses
  • IVF embryos

Disorders that they can identify include cystic fybrosis and Huntingson's disorder. They can use a special piece of DNA called a gene probe. This is a single strand of DNA with bases that will pair with the faulty allele.

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B7.5 Respiration

What is aerobic respiration?

Aerobic respiration happens in cells. In aerobic respiration

  • Oxygen is used
  • Energy is released from food chemicals such as glucose

Glucose  +  Oxygen  --------> Carbon Dioxide  +  Water  ( + energy released  )

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B7.5 Respiration

What happens to the energy released?

The energy released in respiration is used for life processes including movement. It is the energy for the contraction of muscle tissue comes direstly form the breakdowm of ATP. We call ATP the 'energy currency' of living things.

When you exercise, your muscle cless respire faster to provide additional energy for movement. So, they need an increase in the rate of:

  • oxygen supply
  • Glucose supply
  • Carbon dioxide removal

That is why your heat rate and breathing rates increase during exercise. Because factors such as heart rate vary, 'normal' measurements are given within a range.

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B7.5 Respiration

What is anaerobic respiration?

This is the kind of repiration that takes place in muscle cells when they dont get enough oxygen. It is a way of releasing energy without oxygen.

Glucose -------> lactic acid  ( + energy released*)

*aerobic respiration releases more energy per glucose molecule then anaerobic respiration.

In anaerobic respiration, lactic acid builds up in muscles. It makes them feel sore and tired.

Oxygen is needed to break down the lactic acid and realease the energy left in it. The amount of oxygen needed is called the 'oxygen debt'. However, when there is a shortage of oxygen, anaerobic respiration is beneficial for human beings and other organisms.

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B7.6 Circulation

What is in blood?

Human blood contains:

  • a fluid called plasma - that contains water, dissolved substances such as glucose, hormones and waste products.
  • red blood cells containing haemoglobin to carry oxygen
  • white blood cells to fight infection; some make anitbodies and others engulf and digest microorganisms.
  • platelets - fragments of cells that help to clot blood at a wound

What are blood types and why are they important?

These are markers called antigens on the surface of the cells. If an antibody recognizes a foreign atigen, it joins with it. Antibodies destroy cells in various ways. If a person recieving a blood transfusion has antibodies to the sntigens on the donors red blood cells the red blood cells clump together, they block blood vessels and the person dies. So, to avoid clotting, the donor and recipient's blood must be matched.

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B7.6 Circulation

How do we know which blood is safe?

Blood type          Antigens on the cells         Antibodies         will clot blood type...        can recieve blood type

      A                               A                               Anti-B                        B                                         A or B

      B                               B                               Anti-A                        A                                         B or O

    AB                             AB                              None                       None                                  AB, A, B, O

     O                           Neither                   Anti-A, & Anti-B            A, B & AB                                    O

So people with blood type AB blood ( universal recipients ) can recieve blood from anyone.

The red cells in type O blood have no antigens so anyone so anyone can safely recieve type O blood. So we call people with type O blood universal donors.

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B7.6 Circulation

What is your heart like?

Heart ---> artery ---> smaller arteries ---> capillaries ---> small veins ---> veins ---> heart

In one circulation around the body, the blood flows through your heart twice. We call this the double circulation. We need it so the blood:

  • Gains oxygen and loses carbon dioxide in the circulation through the lungs
  • Loses oxygen and gains waste carbon dioxide as it circulates around the rest of the body.

Why are capilleries important?

Capillary walls are only one cell thick, so:

  • Blood pressure can force water and dissloved substances from the blood out into the tissues. This form tissue fluid.
  • Substances such as oxygen, carbon dioxide, glucose and urea can diffuse between the blood and the tissues.
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B7.7 Skeletal system

How do our joints move?

Verterbrates such as humans have an internal skeleton of bone and cartilage for support and movement. Muscles can move bones at a joint only by contraction so they operate in antagonistic pairs. When one muscle of an antagonistic pair contracts the other mucles relaxes.

How do we treat injuries to joints?

Common injuries such as - Sprains (overstretched ligaments), Dislocations (bones out of joint), torn ligaments, and torn tendorns. If you have sprained your ankle, it will be swollen, red or bruised looking and you will find it difficult walking. Treatment is:

Rest - not moving the injured part

Ice - slows blood flow and reduces pain

Compress - bandage to reduce swelling

Elevate - raise to reduce blood flow and drain fluid

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B7.7 Skeletal system

When swelling has gone down you may need physiotheraoy to get the joint and muscles moving again. Strengthening the muscles also reduces the risk of further injury.

Why do doctors and fitness trainers ask so many questions?

Doctors need to know your medical and lifestyle history before they diagnose or treat you. this includes:

  • Your symptoms
  • Your general health such as blood pressure
  • Any medication that you are already on
  • Any previous health problems or treatments
  • Your alcohol or tobacco consumption
  • How much you exercise
  • Your family medical history

Also a fitness trainer needs to know alot of this information before you start a new exercise regime.

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B7.7 Skeletal system

Both need the information:

  • To insure that what they suggest is safe for you
  • To plan a regime for you both with a realistic targets. The plan may be designed to cure you of disease, improve firness, or get you back to normal after a injury or health problem (rehabilitation)
  • As a baseline for monitoring your progress

Keeping accurate records of progress is important. A treatment or an exercise plan may be changed because either it isn't working, or it's causing side effects.

In the case of side effects, treatment may be continued if the benefits are greater than the problems. However, there are often alternative treatments that can be tired.

Doctors and trainers need to make sure that their way of monitoring their patient or client produces reliable data. Following injury, muscles and joints need to be exercised to recover their strength and mobility. You need to be able to describe a set of exercises to treat an injury. This could include stretching the muscle, moving the joint without weight on it, and gentle exercise.

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really good!


If carlsberg could do revision notes ..... (That was good revising)


These have really helped. Thanks!!!


Fab notes! Thanks! :)


amazing notes!!!!!


The best notes on B7 so far, thank you so much! 


blood type A can not accept blood type B but O because O is the universal dOnar but seriously though ammaaaaaazing notes otherwise have helped my students so much

Super Voltage

Thank you very much

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