Plants make their own food by using PHOTOSYNTHESIS

The equations for PHOTOSYNTHESIS is:

Carbon Dioxide + Water - Glucose + Oxygen

The cells in the leaves of plants are small green parts called CHLOROPLASTS. They contain CHLOROPHYLL, a green substance.

During PHOTOSYNTHESIS, light energy is absorbed by the CHLOROPHYLL and the energy is used to convert Carbon Dioxide and Water (from the soil and air) into Glucose. The chemical reaction also produces Oxygen.

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The Process of Photosynthesis

Plants make their own food, by using PHOTOSYNTHESIS.

The equation for PHOTOSYNTHESIS is:

Carbon Dioxide + Water - Glucose and Oxygen

The cells in the leaves of plants are called CHLOROPLASTS. They contain CHLOROPHYLL, a green substance.

During PHOTOSYNTHESIS, light energy is absorbed by the CHLOROPHYLL. This energy is used to convert CARBON DIOXIDE and WATER (from the air and soil) into GLUCOSE. The chemical reaction also produces OXYGEN.

Some of the GLUCOSE that is produced in PHOTOSYNTHESIS, is used immediately. Although a lot it put into storage.

To test that PHOTOSYNTHESIS, has taken place in a plant. You can use IODINE test for STARCH! IODINE is a YELLOWY-BROWN solution, that will turn BLUE, in the presence of STARCH.

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How Are Leaves Adapted For Photosynthesis

The leaves of plants are well adapted, for PHOTOSYNTHESIS becasue:

  • Most leaves are BROAD, they have a LARGE SURFACE AREA, to absorb more LIGHT.
  • They contain CHLOROPHYLL in the CHLOROPLASTS, to absorb LIGHT ENERGY.
  • They have AIR SPACES which allow CARBON DIOXIDE to get to the cells, and OXYGEN to leave them.
  • They have VEINS which supply plenty of WATER to the leaves.
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Photosynthesis Summary Questions

1) Copy and Complete using words below:

Carbon Dioxide          Chlorophyll          Energy          Gas          Glucose          Light          Oxygen          Water

During photosynthesis.....energy is absorbed by.....,a substance found in chloroplasts. This.....is then used to convert.... ......from the air and.....from the soil into a simple sugar called..... . ........is also produced and released as.....

2 a) WHERE does a plant get the CARBON DIOXIDE, WATER and LIGHT that is needs for PHOTOSYNTHESIS?

2b) Work out the path taken by a carbon atom as it moves from being parrt of the CARBON DIOXIDE in the air to being part of a starch molecule in a plant.

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Limiting Factors

LIGHT Probably the most obvious factor affecting PHOTOSYNTHESIS. If there is plenty of LIGHT, then then there can be lots of PHOTOSYNTHESIS. If there is no LIGHT, PHOTOSYNTHESIS will stop regardless of the other extenal conditions. This is why the STOMATA close up at night becasue GASES for PHOTOSYNTHESIS are not needed and water is wasted. 

TEMPERATURE TEMPERATURE affects all CHEMICAL REACTIONS, including PHOTOSYNTHESIS. The hotter the TEMPERATURE, the faster the rate of PHOTOSYNTHESIS. But, PHOTOSYNTHESIS is controlled by ENZYMES and when they get too hot they die. So, when the TEMPERATURE rises above 50 degrees celcius, the rate will decrease, becasue the ENZYMES have DENATURED.

CARBON DIOXIDE:  As CARBON DIOXIDE in the atmosphere increases so does the rate of PHOTOSYNTHESIS, althought there's only 0.04% in the atmosphere so occationally, levels of CARBON DIOXIDE in the atmosphere can limit PHOTOSYNTHESIS.

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Limiting Factors Summary Questions


1b) What are the THREE main LIMITING FACTORS affecting PHOTOSYNTHESIS, in a plant?

2) Which FACTORS do you think would be limiting PHOTOSYNTHESIS in the following situations? In each case, explain why the rate of PHOTOSYNTHESIS, is limited.

a) Plants growing on woodland floor in winter

b) Plants growing on woodland floor in the summer

c) A field of barley first think in the morning

d) The same field later on in the day

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How Plants Use Glucose


Like humans, plants RESPIRE. They use OXYGEN and GLUCOSE to make ENERGY for their cells. CARBON DIOXIDE and WATER are waste products.

Other GLUCOSE is stored as STARCH, because GLUCOSE is soluble in WATER so it could afect the whole water balance, of the whole plant. But STARCH is insoluble so plenty of it can be stored with no effects. 

Some is turned into complex carbohydrates like CELLULOSE- used to create new plant CELL WALLS.

Plants use some of the ENERGY from RESPIRATION to combine SUGARS with other NUTRIENTS (mineral ions) from the SOIL to make ALMINO ACIDS.

These ALMINO ACIDS are then build up into PROTEINS to be used in CELLS.

ENERGY from RESPIRATION is also used to build up FATS and OILS to make a FOOD STORE for the seeds.

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How Plants Use Glucose


Plants make food by PHOTOSYNTHESIS, in their LEAVES. But, food is needed all over the leaf, so it's moved around the plant in a SPECIAL TRANSPORT SYSTEM

There are two different TRANSPORT SYSTEMS in plants.

The PHLOEM - made of living tissue, transports SUGARS made from PHOTOSYNTHESIS, to the rest of the plant.

PHLOEM tubes have THIN walls and LIVING cells.

The XYLEM - the other transport tissue, it carries WATER and MINERAL ions, from the SOIL around the plant.

XYLEM tubes have THICK, STRONG walls and are NOT LIVING.

A VASCULAR BUNDLE contains PHLOEM and XYLEM with CAMBIUM cells between them.


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Making The Most of Photosynthesis

Plant growers try to give their plants the best conditions for growth by controlling the enviroment:

Greenhouses and polytunnels can be constructed to grow plants in an enclosed space, if the greenhouse or polytunnel have lighting or heaters then the rate of PHOTOSYNTHESIS will increase.

Although, this may stop if the TEMPERATURE or LIGHT INTENSITY is too high. If CARBON DIOXIDE is added the polytunnel or greenhouse, then the rate of PHOTOSYNTHESIS will also increase.

NITRATE IONS, can also be added to the soil to ensure plants can make PROTEINS needed for healthy growth.

It can be expensive to provide a suitable TEMPERATURE, LIGHT and CARBON DIOXIDE. So the grower must compare the BIOMASS of the plants grown inside and outside.

They must evaluate the benefits of increasing growth with the increased cost of heating, lighting and providing carbon dioxide.   

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Pyramids of Biomass

Some of the light is captured in the CHLOROPHYLL of green plants. It is used in PHOTOSYNTHESIS. The new plant material which is stored, is called BIOMASS.


The ENERGY in the BIOMASS made from plants, is passed on in FOOD CHAINS.  No matter how long the FOOD CHAIN is the original ENERGY source is always from the sun.

FOOD CHAINS normally have more PRODUCERS than PRIMARY CONSUMERS, and so on. If you can count the number of ORGANISMS at each level you can produce a PYRAMID OF NUMBERS.

In a PYRAMID OF BIOMASS the BIOMASS at each stage of the FOOD CHAIN is less than it was at the previous stage, because:

  • Not all the ORGANISMS are eaten, by the above stage
  • Some material is passed out as WASTE
  • When a HERBAVORE eats a plant, it is used for RESPIRATION so this is not absorbed by the CARNIVORE, when the HERBAVORE is eaten.
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Pyramids of Biomass Summary Questions

1) What is BIOMASS and why is a PYRAMID OF BIOMASS more useful for showing what is happening in a FOOD CHAIN than a PYRAMID OF NUMBERS?

2) Organism:                          Biomass, dry mass (g):

    Grass                                 100 000

    Sheep                                 5000

    Sheep Ticks                        30

a) Draw a PYRAMID of BIOMASS and what would you expect the PYRAMID OF NUMBERS to look like?

b) Draw the PYRAMIDS of NUMBERS and BIOMASS for:

i) Stinging nettles- Catterpillers- Robin     ii) Marine plants- Small fish- Large fish- Seals- Polar bears

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Energy Lost As Waste

The amounts of BIOMASS and ENERGY contained in LIVING THINGS always gets less at each stage of the FOOD CHAIN, from PLANTS onwards. Only a small amount of BIOMASS is turned into new animal material.

The Energy Lost in Waste:

HERBAVORES cannot diggest all the plant material they eat. The material they can't digest is passed out as FAECES.

CARNEVORES feed less often, as their FOOD is easier to digest so they produce less WASTE. But some BIOMASS is lost in their FAECES; HOOVES, CLAWS and TEETH.

When an animal eats more protein than it needs, the excess is broken down and past out as UREA in the URINE.

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Energy Losses

Energy Loss Due to Movement:

Part of the BIOMASS eaten is used for RESPIRATION, in the cells. RESPIRATION provides ENERGY for LIVING PROCESSES.

MOVEMENT uses a great deal of ENERGY. The muscles need ENERGY to contract, so the more the animal moves the more ENERGY (and BIOMASS for RESPIRATION) they need. The muscles produce HEAT as a WASTE product!

Maintaining A Constant Body Temperature:

Most energy animals produce from their FOOD in RESPIRATION is lost as HEAT to the surroundings. Some of this heat is produced by the MUSCLES envolved in MOVEMENT.

Because animals are WARM BLOODED they lose more HEAT to keep their bodies at a CONSTANT TEMPERATURE. They use up energy all the time. To keep WARM when it's COLD and to stay COOL when it's HOT.

Due to this WARM BlOODED animals have to eat more than COLD BLOODED, to get the same increase in BIOMASS

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Energy Losses Summary Questions

1) Copy and complete using the words below:

Biomass           Body Temperature         Energy          Food Chain          Growth           Movement          Producers          Respiration          Waste

The amounts of.... and .....contained in living things always gets less at each stage of a ..... ..... from.... onwards. Biomass is lost as..... products and used to produce energy in..... . This is used for..... and to control..... ...... . Only a small amount is used for ..... .

2) Explain why so much of the energy from the sun whihc land on the suragce of the earth is not turned into biomass in animals.

3) Why do warm-blooked animals need to eat more food than cold-blooded ones of the same size if they are to put on weight?

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Energy in Food Production

PYRAMIDS OF BIOMASS clearly show us that the ORGANISMS at each stage of the FOOD CHAIN contain less material and therefore less ENERGY.

Food Chains in Food Production:

In the developed world our diet consists heavilly of MEAT and other ANIMAL PRODUCTS. But by the time the ANIMALS we use to produce our food have used up the majority of the energy from the plant.

So in many cases we have to add another EXTRA LAYER into the FOOD CHAIN. What could have been BIOMASS for us is WASTED on animals.

As the area to grow plants is limited on the earth the most ENERGY EFFICIENT way to use this food is to grow plants and eat them directly. If we only ate plants in theory there would be enough food for everyone.

But the more stages we introduce the less energy getting to us at the end of the FOOD CHAIN. So less food to go round the population.

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Energy in Food Production

People want ANIMAL PRODUCTS as cheep as possible, so farmers want more BIOMASS out of their ANIMALS without feeding them any more. They do this by:

  • Limiting the movement of the animals. They lose a lot of energy in contracting their muscles, so if they're not moving there will be more BIOMASS available from FOOD for GROWTH
  • Controlling the temperature of the surroundings. The animals will not WASTE and much ENERGY keeping warm. Leaving more BIOMASS spare for GROWTH.

Animals are kept in restricted rooms and with heaters on. It also speeds up the rearing time of animals particularly birds.

INTENSIVE FARMING METHODS are used becasue there is a steady increase in demand for CHEAP MEAT and ANIMAL PRODUCTS

But these animals live very UNNATURAL and RESTRICTED lives. So there has been a backlash against the conditions used. Many people say they would be willing to eat less meat less often and pay more if the animals were raised more NATURALLY.

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The Decay Process

Many trees shed their LEAVES each year and most animals produce DROPPINGS once a day. ANIMALS and PLANTS will die EVENTUALLY. These MATERIALS will be recycled into the ENVIROMENT, due to DECOMPOSERS.

The Decay Process:


  • DETRIUS FEEDERS, like maggots and some worms start the process. They eat dead animals and produce waste material
  • The FUNGI and BACTERIA then digest everything- dead animals, plants, DETRIUS FEEDERS plus their waste. These nutrients are used to GROW and REPRODUCE

When we say things DECAY, they are actually being broken down and digested by microoganisms. The process of decay makes sure the soil remains FERTILE and plants can grow.

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The Conditions and Importance of Decay

The speed at which things DECAY depends partly on the TEMPERATUR. The CHEMICAL REACTIONS in MICROOGANISMS are like those in most other living things. They work FASTER in WARM conditions. 

However, they SLOW if it's too cold and will STOP if it's too HOT as the ENZYMES DENATURE.

Most MICROORGANSMS also grow better in MOIST conditions. The MOISTURE makes it easier to disolve the their FOOD and prevents them from DRYING OUT.

They also need OXYGEN to RESPIRE, GROW and REPRODUCE. This is why DECAY takes place more rapidly, when there is plenty of OXYGEN available.

The Importance of Decay In Recycling:

In SEWAGE TREATMENT PLANTS human use MICROOGANISMS to break down bodily waste and make it safe enough to be released into the sea.

Humans also use COMPOST HEAPS to break down plant material

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The Carbon Cycle

CARBON is constantly cycled through the ENVIROMENT

Photosynthesis:    Carbon Dioxide + Water - Glucose + Oxygen

Green plants use CARBON DIOXIDE in PHOTOSYNTHESIS. They use the SUGAR produced to make BIOMASS and when they're eaten by other animals this is passed on. The CARBON goes on to be the CARBOHYDRATES, PROTEINS and FATS in their bodies

Respiration:          Glucose + Oxygen - Energy + Carbon Dioxide

Animals and plants are constantly RESPIRING they use OXYGEN and GLUCOSE to provide ENERGY for their cells. CARBON DIOXIDE is a waste product.

Combustion:         Fossil Fuel (or Wood) + Oxygen - Carbon Dioxide + Water

Fossil fuels contain CARBON. But when they are burnt some of the CARBON is released back into the atmosphere.

Energy Transfers: Carbon made from reclycling plants as NUTRIENTS. Transfered as heat or into Decomposers

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Carbon Cycle


a) What is the Carbon Cycle?

b) What are the main processes involved?

c) Why is the Carbon Cycle so important for life on earth?


Explain carefully how a) Carbon and b) Energy are transfered through an ecosystem?

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The Carbon Cycle

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Proteins, Catalyst and Enzymes

Protein Molecules are made of long chains of AMINO ACIDS. The LONG CHAINS are folded to produce certain shapes. The shape of a PROTEIN depends on its structure.

Proteins can be:

  • Structural componants of tissues, such as mussle
  • hormones
  • antibodies

Chemical reactions in cells are controlled by proteins called ENZYMES

  • ENZYMES are BIOLOGICAL CATALYSTS- they speed up reactions
  • They are large proteins, and the shape has an area where other molecules can fit- THE ACTIVE SITE
  • The SUBSTRATE in a reaction can be held in THE ACTIVE SSITE and broken down, or connected to another molecule
  • ENZYMES can: build molecules from smaller molecules, change molecules and break down large molecules
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Factors Affecting Enzyme Action

Similar to other reactions when the TEMPERATURE is increased

  • Reactions happen QUICKER when it's WARMER. At higher TEMPERATURES the molecules more around more quickly and have more energy to colide more often
  • The rate of an enzyme-controlled reaction increases as the temperature rises- but only until the point where the COMPLEX PROTEIN structure of an ENZYME breaks down. Then the ENZYME DENATURES.
  • Each enzyme works best at a PARTICULAR pH value. Some work best in acid conditions, like the STOMACH. But others need NEUTRAL or ALKALINE conditions
  • If the pH is too ACIDIC or ALKALINE for the ENZYME, then the ACTIVE SITE could change shape. Then the ENZYME becomes DENATURED.
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Enzymes in Digestion

Digestive ENZYMES are produced by specialised cells in the glands and the LINING OF THE GUT. The ENZYMES pass out of the cells and come into contact with the FOOD. Digestion is the break down of large, insoluble molecules into smaller ones.

Each reaction is PROTEIN specific:

  • AMYLASE (a CARBOHYDRASE). It is produced by the SALIVARY glands, the PANCREAS and the SMALL INTESTINE. AMYLASE catalyses the digestion of STARCH into SMALLER SUGARS in the MOUTH and SMALL INTESTINE
  • PROTESE - produced by the STOMACH, the PANCREAS and THE the SMALL INTESTINE. PROTESE catalyses the breakdown of PROTEINS into ALMINO ACIDS in the STOMACH and SMALL INTESTINE
  • LIPASE - produced by the PANCREAS and SMALL INTESTINE. LIPASE catalysised the breakdown of LIPIDS (fats and oils) to FATTY ACIDS and GLYCEROL.
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Speeding up Digestion

PROTESE enzymes work best in the STOMACH, in ACIDIC conditions. GLANDS in the STOMACH produce HYDROCHLORIC ACID to create ACIDIC conditions

AMYLASE and LIPASE work in the SMALL INTESTINE. They work best in SLIGHTLY ALKALINE conditions.

The LIVER produces BILE, that is stored in the GALL BLADDER. This ALKALINE BILE is squirted into the SMALL INTESTINE and NEUTRALISES the STOMACH ACID. The conditions are made SLIGHTLY ALKALINE

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Aerobic Respiration

Aerobic RESPIRATION is constantly taking place in animals and plant. The process uses OXYGEN to breakdown the GLUCOSE and release ENERGY and CARBON DIOXIDE and WATER as waste products.

Most of the chemical reactions take place in the MITOCHONDIA and are controlled by ENZYMES


The energy realeased by the process can be used to:

  • Build larger molecules from smaller ones
  • Enable muscle contraction
  • Maintain a constant body temperatire
  • Build SUGARS, NITRATES and other NUTRIENTS into ALMINO ACIDS and PROTEINS (in plants)
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The Effect of Exercise on the Body

When you exercise, your muscles need more energy so that they can CONTRACT

You have to increase the rate at which OXYGEN and GLUCOSE reach the MUSCLE cells for AEROBIC RESPIRATION. You also need to remove extra waste CARBON DIOXIDE produced more quickly.

To do this, the HEART RATE increases and the blood vessels supplying the muscles DIALATE. This allows more BLOOD rich in OXYGEN and GLUCOSE to reach the muscles and RESPIRE

Your BREATHING RATE also increases and the DEPTH OF EACH BREATH. This allows a greater uptake of OXYGEN and release of CARBON DIOXIDE

Muscles store glucose as GLYCOGEN. This GLYCOGEN can be converted into GLUCOSE for use during exercise.

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Anaerobic Respiration

If you use your muscles for a long period of time, they will get tired and stop working efficiently. When your muscles cannot get enough OXYGEN for AEROBIC RESPIRATION they RESPIRE ANAEROBICALLY.

In ANAEROBIC RESPIRATION the GLUCOSE is not completely broken down and lactic acid is produced.

  • Less energy is released
  • One cause of muscle fatigue is a build up of LACTIC ACID
  • Blood flowing through muscles removes LACTIC ACID

When the exercise has finished this LACTIC ACID must be completely broken down. This requires a lot of OXYGEN. The extra OXYGEN needed is known as the 'OXYGEN DEBT'. Eventually, the OXYGEN oxydises LACTIC ACID into CARBON DIOXIDE and WATER.

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End of Chapter Questions

1. What does 'AEROBIC' mean?

2. What is meant by 'ANAEROBIC RESPIRATION'?

3. What do muscle cells need more of during exercise?

4. What are the 2 waste product of AEROBIC respiration?

5. Which substance stored in cells can be converted into GLUCOSE?

6. What is the word equation for AEROBIC RESPIRATION?

7. Why do muscles become FATIGUED during exercise?

8. What changes occur in BREATHING and HEART RATE during exercise?

9. Why do blood vessles in the muscles dialate?

10. What is meant by 'OXYGEN DEBT'?

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Cell Division and Growth

Cell division is needed for the growth of an organsim, or for repair of damaged tissues.

MITOSIS- results in 2 identical cells being produced from the orginal cell.

The CHROMOSOMES contain ALLELES (genes) which must be passed on to each new cell.

A copy of each CHROMOSOME is made before the cell divides and one of each CHROMOSOME goes into each new cell.

In early development of animal and plant embreyos the cells are UNSPECIALISED and are called STEM CELLS.

Most animal cells DIFFERENCIATE early in development and cell division is for principally GROWTH and REPAIR

Plant cells can DIFFERENCIATE throughout the life of a plant as it continues to grow.

Cells of OFFSPRING produced by ASEXUAL reproduction are produced by MITOSIS from the parent cell. They contain the same ALLELES as the PARENTS.

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Cell Division and Growth

Cell division is needed for the growth of an organsim, or for repair of damaged tissues.

MITOSIS- results in 2 identical cells being produced from the orginal cell.

The CHROMOSOMES contain ALLELES (genes) which must be passed on to each new cell.

A copy of each CHROMOSOME is made before the cell divides and one of each CHROMOSOME goes into each new cell.

In early development of animal and plant embreyos the cells are UNSPECIALISED and are called STEM CELLS.

Most animal cells DIFFERENCIATE early in development and cell division is for principally GROWTH and REPAIR

Plant cells can DIFFERENCIATE throughout the life of a plant as it continues to grow.

Cells of OFFSPRING produced by ASEXUAL reproduction are produced by MITOSIS from the parent cell. They contain the same ALLELES as the PARENTS.

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Cell Division

The normal body cell had four CHROMOSOMES in two pairs

As CELL DIVISION starts, a copy of each CHROMOSOME is made

The cell then DIVIDES into TWO, to from TWO daughter cells. Each DAUGHTER CELL has a nucleus containing four CHROMOSOMES in two pairs (IDENTICAL to the original parent cell)

Two identical cells are formed by simple division that takes place during MITOSIS. There are actually 23 pairs of CHROMOSOMES.

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Cell Division in Sexual Reproduction

Cells in REPRODUCTIVE ORGANS (testies and ovaries) divide by MEIOSIS to from GAMETES (sex cells). In humans these GAMETES are SPERM and OVA

Each GAMETE has only one CHROMOSOME from each original pair. All the cells are different from eachother and their parent cell

Sexual Reproduction results in VARIENCE as the GAMETE from each parent fuse. Half the genetic information comes from the father and half from the mother.

When GAMETES join at FERTILISATION, a single body cell with new pairs of CHROMOSOMES is formed.

A new INDIVIDUAL then develops by the cell repeatedly dividing using MEIOSIS.

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Cell Division in Sexual Reproduction


  • Before division, a copy of each CHROMOSOME is made
  • The cell then DIVIDES TWICE to form four GAMETES
  • Each GAMETE has a single set of CHROMOSOMES each with a different combination of genes

The formation of GAMETES in the OVARIES and TESTIES requires MEIOSIS to have the CHROMOSOME number.

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Stem Cells


They are found in the human EMBREYO and in ADULT BONE MARROW

STEM CELLS change into all the different types of body cells- NERVE CELLS, MUSCLE CELLS etc.


Layers of cells in the EMBREYO differentciate into all the cells the body needs

STEM CELLS in the ADULT BONE MARROW can change into many different type of cell. The cells formed could then be used to treat conditions, such as PARALYSIS by differenciating into new NERVE CELLS.

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From Mendel to DNA

Gregor Mendel was a monk who worked out how CHARACTERISTICS were inherited. Mendel was the first person to suggest the idea of separately INHERITED 'FACTORS'

It took a long time for Mendel's ideas to be accepted. That was becasue scientists didnt know about CHROMOSOMES or GENES until Mendel had died.

Mendel's factors are now called GENES. GENES are found on CHROMOSOMES

CHROMOSOMES are made of DNA which is a very long molecule with a DOUBLE HELIX STRUCTURE.

GENES are short sections of DNA

Every person, except for identical twins, has different DNA. They can be identified by the DNA fingerprint.

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Inheritance in Action

  • Human beings have 23 pairs of CHROMOSOMES, one pair are the SEX CHROMOSOMES, human females have two X CHOMOSOMES (**) and males have and X and a Y CHROMOSOME (XY0
  • Genes controlling the same CHARACTERISTICS are called ALLELES
  • If an ALLELE masks the effect of another it is DOMINANT. If the ALLELE is masked by another it is said to be RECESSIVE
  • Genetic diagrams, including family trees, illustrate how ALLELES and CHARACTERISTICS are inherited.

Punnet squares are used to display ALLELE symbols

PHENOTYPE- Physical appearance of characteristic e.g. dimples

GENOTYPE- Genetic make up e.g. which ALLELES does the individual inherrit

Homozygous-  Both the ALLELES are the same DD, homozygous dominant or dd homozygous recessive.

Heterozygous- the two ALLELES are different Dd

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Inherited Conditions in Humans

There are many GENETIC DISORDERS, caused by dominant and recessive ALLELES

If the ALLELE is dominant the person has to only inherit one ALLELE to have the disorder- like POLYDACTYLY where the baby is born with extra fingers of toes

If an ALLELE is recessive the person inherit two to have the disorder.

CYSTIC FIBROSIS is casue by the recessive ALLELE. It affects the cell membranes and causes production of sticky mucus. The mucus can affect several organs including th LUNGS and PANCREAS.

The disorder can be passed on from two parents that don't have the disorder, they are described as carriers.

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Stem cells and Embreyos -science and ethics

Adult STEM CELLS are useful in treating some disorders like leukaemia

More recently, doctors have investigated that STEM CELLS have the ability to DIFFERENCIATE into a wide variety of cells

Embreyonic stem cells are taken from spare embreyos from IVF or created from adult cells or may be taken from the UMBILICAL CORD of newborn babies. Emberyonic STEM CELLS can be used t grow new tissues and organs needed for a transplant

Some people are concerned about the uses as the research is experimental, the embreyos have the potential to be babies but are destroyed. The embreyo cannot give permission and the research is expensive.

Embreyo SCREENING involves test to diagnose disorders before the baby is born. The results of the tests give parent some choices, and they may terminate the pregnancy. Other parents see this as unethical

In IVF only healthy embreyos are used, those with faulty genes are destroyed. Some people see this as unethical 

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End of Chapter Questions

1. Why do cells divide by MITOSIS/

2. How many CHROMOSOMES does a human have in each body cell?

3. What type of cell division produces sex cells?

4. What molecule are genes made of?

5. What are ALLELES?

6. Why does SEXUAL REPRODUCTION result in variation?

7. Explain why offspring produced by asexual reproduction are genetically identical?

8. What is meant by Genotype?

9. What do we mean by a 'heterozygous' individual?

10. What are the chances of having a child with poludactyly if one parent it heterozygous and the other is homozygous recessive?

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The Origins of life of Earth

It is believed the earth is 4500 million years old and that life began 3500 million years ago. There is a debate as to whether the first life developed due to the earths conditions, or whether simple life forms arrived from another planet.

We can date rocks and the organisms found in them so we can date when different organisms existed.

Fossils can be formed in different ways:

  • From the hard parts of animals that dont decay
  • From parts of organisms that have not decayed due to conditions, for decay was absent
  • When parts of the organism have been replaced by material
  • As preserved traces of organisms

Most organisms that have does did not leave a fossil becasue the conditions for fossil formation weren't present.

Many early life forms  had soft bodies for there are few traces and traces left are likely to have been destroyed by geographical activiy.

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Exploring Fossil Evidence

The fossil record is incomplete but a lot can be told from the fossils which exist. Some organisms have changed a lot while other haven't.

EXTINCTION- means a species which once existed has completely died out

This can be casued by a number of factors:

  • A new disease may have killed all member of the species
  • The enviroments geographical changes
  • New disease may be introduced
  • A new predator may evolve
  • A competitor may evole and eat all of the food
  • A single catestrophic event may occur, in the habitat
  • Natural changes in species occur over time
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More About Extinction

  •  Climate change is an important influence. A species suited to a hot enviroment may hav become extincted during  the ice age. It may make it too hot or cold, or wet or dry, for a species and reduce its food supply

Fossil evidence shows that there were mass EXTINCTIONS on aglobal scale. Many died out over a period of several million years- a short time.

  • The habitat where the species lived may have been destroyed by a catestrophic event, like a volcanic erruption. The enviroment may have changed following the collision between a giant asteroid and earth

The EXTINCTION of dinosaurs have puzzled many scientist, different ideas have been suggested:              

  • The collision of a giant asteroid caused catestophic events like fires, volcanos, landslides and tsunamis. The dust from these rose and covered the sun causing darkness and lower temperatures, resulting in no plants growing. The extinction was a slower process due to the sea ice meling and cooling the temperature by 9 degrees- less planton and less food
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Isolation and Evalution of New Species

New species can arise from existing species if the group is ISOLATED

GEOGRAPHICAL ISOLATION could occur if an island separates them from the mainland or a new river separates two areas. Mountain ranges and old craters can ISOLATE organisms

These organisms may be exposed to different climates, food ability of predators. Natural Selection, will occur in both. If species are brought together and cannot inbreed, we say they belong to TWO DIFFERENT SPECIES.


  • New species can occur following the ISOLATION of two species
  • Each population has a wide range of ALLELES that control their CHARACTERISTICS
  • NATURAL SELECTION will occur in each population
  • If the enviroment, food supply and predators are different for each population, they will evolve differently
  • Speciation has occured when the two populations can no longer breed.
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End of Chapter Questions

1. How old is the earth?

2. When do we think life began?

3. How are fossils dated

4. Why are there no fossils of early life forms?

5. What is the shortest way to represent 3 billion in numbers?

6. How might a knew competitor cause extinction of species?

7. Suggest two ways that people can cause extinction of some species?

8. What are the two main ideas put forward for the EXTINCTION of dinosaurs?


10. What are the stages in SPECIATION?

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