Biology B2 Revision Notes

Notes for Biology unit 2 exam, BLY2H

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Animal Cells:

  • Mitochondria- Release energy during respiration.
  • Ribosomes- Makes Proteins.
  • Cell Membrane- Allows selective passage of gases, water and minerals.
  • Nucleus- Stores genetic infromation and controls activities.
  • Cytoplasm- Liquid gel in which chemical reactions take place.

Plant Cells:

  • Nucleus.
  • Cytoplasm.
  • Cellulose Cell Wall- Gives structure and strength. Also fixes energy in Photosynthesis.
  • Cell Membrane.
  • Chloroplasts- Contain chlorophyll.
  • Mithochondria.
  • Ribosomes.
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Fat Cell:

  • Store any extra fat in the body.
  • Animals and humans use this store when there is a shortage of food.
  • Their three main adaptations are:

1. They have very little normal cytoplasm and so they have room for large amounts of fat.

2. They use very little energy and so need very few mitochondria.

3. When they fill up with fat, they expand up to 1000 times its original size.

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Specialisation Continued

Cone Cell from Human Eye:

  • Found in light sensitive part of the eye, "the retina".
  • They allow you to see colour.
  • Their three main adaptations are:

1. Visual pigment in the outer segment changes chemically in coloured light. It has to be changed back again and this uses energy.

2. The many mitochondria in the middle segment produce energy which means the visual pigment can reform and so we can continually see in colour.

3. The specialized nerve ending/synapse connects to the optic nerve which carries impules to your brain. An impulse is triggered across the synapse when visual pigment changes with coloured light.

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Specialisation Continued

Root Hair Cell:

  • They are found close to the tips of growing roots and enable plants to take in water.
  • They have three main adaptations which are:

1. They increase surface area so water can move into the cell.

2. The large permanent vacuole affects the movement of water from the soil across the root hair cell.

3. Are always positioned close to the xylem tissue that carries water to the rest of the plant.

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Specialisation Continued

Sperm Cells:

  • Are released a long way away from the egg they are fertilising and they contain the genetic information from the male parent to pass onto offspring.
  • They move through the female reproductive system to reach the egg. They then break into the egg.
  • Three main adaptations of sperm cells are:

1. They have long tails with muscle-like proteins in them so they can swim towards the egg.

2. The mitochondria in the middle section produce energy for the tail to work.

3. The acrosome stores digestive enzymes which are used for breaking down the outer layers of the egg.

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Diffusion is the net movement of particles of a gas or a solute from an area of high concentration to an area of low concentration as a result of the random movement of the particles.

A cut in water looks worse than a cut on land because the blood diffuses in the water and the particles disperse in the water and so it appears that there is more blood then there actaully is.

In the human body there are organs that increase their surface area to increase the rate of diffusion. Such as: Alveoli in the lungs and the small intestines. This is also true in plants: In root hair cells and thin leaves.

Diffusion takes place faster in an increased temperature because there is more thermal energy present.

Cells have folded membranes so they can expand when needed and so increases the rate of diffusion.

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Osmosis the movement of water from a high concentration of water to a lower concentration through a partially permeable membrane.

Osmosis helps maintain the body cells at the same concentration because water will move to where there is a lower concentration.

  • Osmosis is a special case of diffusion.
  • A Partially Permeable Membrane is a material that only allows certain substances to pass through.
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Carbon Dioxide + Water + Light energy from the sun = Glucose + Water

  • Energy fixation.
  • Energy transformation.
  • Involves light and heat energy which is chemical.
  • Plants provide chlorophyll.
  • Glucose comes from respiration.
  • Respiration takes place in the mitochondria.
  • Glucose turns into starch and is then stored.
  • Stored starch = Biomass.

What Slows Down The Process of Photosynthesis?

  • Temperature.
  • Amount of light.
  • Amount of chlorphyll.
  • CO2 concentration.
  • Water concentration.
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Photosynthesis Continued

During photosynthesis light energy is absorbed by chlorophyll, a substance found in the chloroplasts. This energy is then used to convert carbon dioxide from the air and water from the soil into a simple sugar called starch. Oxygen is also produced and released as a gas.

Carbon comes from CO2 in the air. This enters the leaf through stomata at the bottom of the leaves using the process of diffusion. This is then absorbed into the spongey layer, then diffuses into palisade cells. It then goes into the chlorophyll and into the process of photosynthesis.

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Photosynthesis Continued

1. Oxygen is released by the green leaves.

2. Glucose is manufactured by green leaves.

3. Energy for photosynthesis comes from the sun.

4. Water is absorbed by the roots in the soil.

5. Carbon Dioxide is absorbed by the leaves.

6. Starch is stored as food in seeds.

7. Chloroplasts in cells are found in green leaves.

8. Minerals are absorbed by the roots.

9. Chlorophyll is found in green leaves.

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Water Movement In Plants

  • Only occurs from root to leaf.
  • One direction.
  • Travels to leaf through transpiration flow.

Water moves into root through root hair cells by osmosis. It moves from the roots to the leaves by transpiration flow. This process takes place through the xylem. Xylem are bundles of dead tissue found in the stem.

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How Plants Use Glucose

Plants make glucose when they photosynthesise. Some of the glucose produced is used by the cells of the plant for respiration which goes on twenty-four hours a day. It provides energy for cell functions, reproduction and growth. Some is converted to starch for storage.

Plants also use glucose to make amino acids when combinde with other nutrients and for cellulose to make new plant cell walls.

The glucose is converted into starch because starch is insoluble and so it can be stored in large amounts as it doesn't dissolve in water, leaving the balance of the plant untouched.

Starch is stored in tubers and bulbs that are produced by the plant. If you were to boil a piece of potato and then add iodine to it, it will go blue/black in colour due to the presence of starch.

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Pyramids of Numbers and Biomass

  • Arrows in a food chain show the direction of the movement of energy.
  • A pyramid of numbers is not always a pyramid shape.
  • Biomass is the mass of living material in an organism.
  • Pyramids of biomass are the shape they are as energy is not transferred 100%.

A pyramid of biomass is more useful for showing what is happening in a food chain as it shows the amount of energy that is being transferred.

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Energy Loss

In animals that are herbivores, a large amount of energy is lost as faeces. In cold-blooded animals, there is little loss due to heat production.

The amounts of energy and biomass contained in living things always gets less at each stage of a food chain from producers onwards. Biomass is lost as waste products and used to produce energy in respiration. This is used for movement and to control body temperature. Only a small amount is used for growth.

Some warm-blooded animals need to eat more than a cold-blooded animal of the same size because they need to keep their body temperature constant and a lot of energy is lost by doing this.

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Energy in Food Farming

  • All energy on Earth comes from the sun as light and heat.
  • Energy is transferred to plants where it becomes chemical energy.
  • Farming involves the transfer of sun energy into chemical energy for food.

If people ate less meat and more plant material humans would consume far more biomass as less energy would be lost due to the fact that the energy wouldn't be lost at each stage of the food chain for movement, respiration and excretion.

In intensive farming, animals are restricted from moving much and are kept indoors so energy is not lost through movement (kinetic energy) or through the animal trying to maintain a constant body temperature (thermal energy).

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  • Living organisms remove nutrients from the environment as they grow. They return them when they die through the action of the decomposers.
  • Dead materials decay because they are broken down (digested) by micro-organisms.
  • Decomposers work more quickly in warm, moist conditions. Many of them also need a good supply of oxygen.
  • The decay process releases substances which plants need to grow.
  • In a stable community the processes that remove materials (particularly plant growth) are balanced by the processes which return materials.

Warmth is needed as the enzymes will stop working if it's too cold, however, it can't be too warm otherwise the enzymes will become denatured. Moisture helps them to grow quicker and makes it easier to dissolve food as well as preventing them from drying out. Decomposers respire and so need oxygen in order for them to release energy, grow and reporoduce.

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The Carbon Cycle

  • Green plants use carbon dioxide in photosynthesis.
  • Respiration adds carbon dioxide to the atmosphere.
  • Fossil fuels represent a huge (but decreasing) store of carbon.
  • Energy is transferred from plants to animals to decomposers.
  • Respiration releases energy to the environment in the form of heat.

Carbon is transferred through an ecosystem by being stored in fossil fuels, limestone and marine organisms. It is released into the atmosphere when burnt as carbon dioxide. Then plants use it for photosynthesis. Then it is respired and released back into the atmosphere by living organisms.

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  • An enzyme is a biological catalyst. This means that it is found in living systems.
  • A catalyst speeds up the rate of a chemical reaction without changing the end product or being used up.
  • Enzymes catalyse every reaction in living systems.
  • Enzymes are chemicals (proteins made up of amino acids) therefore, enzymes CANNOT DIE, they are DENATURED.
  • The enzyme reaction takes place at the "active site". The reactants must fit into this site.
  • In an enzyme reaction the reactants are called substances.
  • "Activation energy" is the energy needed for a chemical reaction to take place.
  • The structure of the enzyme is very important as the reaction will only work if the enzyme and substance fit together like a rectangle.
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Speeding Up Digestion

  • The enzymes of the stomach work best in acidic conditions.
  • The enzymes made in the pancreas and the small intestine work best in alkaline condidtions.
  • Bile produced by the liver neutralises acid and emulsifies fats.

Bile is an alkaline liquid produced by your liver. It is stored in the gall bladder and released onto food as it comes into the small intestine. It neutralises the acidic food from the stomach and makes it alkaline.

The protease from the stomach works best at pH3.

Your stomach produces a concentration of hydrochloric acid to make it pH2, mucus is also produced to protect the lining of the stomach and prevent stomach ulsars.

Factors which effect the rate of enzyme action are: Temperature, concentration of enzyme, pH and surface area.

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Industrial Uses of Enzymes

Three enzymes in the food industry are:

  • Proteases pre-digest some protein in food.
  • Carbohydrases convert starch into sugar.
  • Isomerase converts glucose syrup into fructose syrup.

Biological washing powders are more effective than non-biological in lower temperatures because the optimum temperature for biological powder is lower and so saves electricity. The lipases and proteases in it break down food, sweat, blood and grass.

Some micro-organisms produce enzymes which pass out of the cells and can be used in different ways.

Biological detergents may contain lipases and protease.

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Advantages and Disadvantages of Enzymes in Industr


  • They catalyse reactions at low temperatures and "normal" pressure.
  • Using the enzyme is more efficient than using the whole organism.


  • Costs a lot of money to build chemical plants and to supply them with heating and pressure.
  • Enzymes are very sensitive to their surroundings. Temperature must be kept quite low (below 45 degrees celsius) and pH levels must be closely monitored. It costs a lot to control these conditions.
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Aerobic Respiration

  • Energy is released from glucose by a process known as respiration.
  • During respiration chemical reactions take place inside the mitochondria in the cells of your body.
  • When glucose reacts with oxygen, energy is released
  • Carbon dioxide and water are formed as waste products.
  • The process is known as aerobic respiration because it used oxygen from the air.

Mithochondria are so important as they provide energy for all the functions of your cells. They are tiny and rod-shaped with a folded inner membrane which provides a larger surface area for the enzymes in aerobic respiration.

Three main uses of the energy released in your body during aerobic respiration are: 1.To build up large molecules from smaller ones to make new cell material you will stop growing if you don't get enough energy 2. to contract muscles, you won't want to move otherwise 3. to control body temperature because if you don't eat enough you begin to get cold.

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Controlling Internal Conditions

Homeostasis is the maintenance of a constant internal environment.

  • Temperature.
  • pH, needs to be slightly acidic but more or less neutral.
  • Sugar levels.
  • Salt levels.
  • Water levels.
  • Ion levels, for example sodium, potassium and chloride.

Excretion is the removal of metabolic waste. Three main methods of excretion are: 1. sweating 2. urination 3. exhalation.

The internal environment of your body is kept relatively constant by a whole range of processes which make up homeostasis. Waste products such as urea and CO2 have to be removed from you blood all the time. The water and ion concentration of your blood are constantly controlled and so is your blood sugar level. Your body temperature is kept the same so your enzymes work effectively.

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Controlling Internal Conditions Continued

Carbon dioxide is formed during cellular respiration. Every cell in your body respires and so produces CO2. You must remove it otherwise it would get dissolved into the cytoplasm of you cells and would affect the pH. It moves out of your cells and into your blood. Your bloodstram carries it back to your lungs. You then exhale it.

Urea is produced in your liver when excess amino acids are broken down. When you eat more protein then you need or when body tissues are worn out, the extra protein has to be broken down. If urea levels build up in your blood it will cause a lot of damage. Urea is filtered out by your kidneys. It is then removed in your urine.

Exercise would affect internal conditions because in order for your muscles to move you must areobically respire, producing H2O and CO2. These would then mix together to make "carbonic acid" and therefore, would alter pH levels. MUSCLES NEED ENERGY TO MOVE, PRODUCED BY RESPIRATION. You lose oxygen and sugar.

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Controlling Body Temperature

  • It isimportant to maintain a body temperature of 37 degrees celsius because this is when the enzymes work best.
  • The thermoregulatory centre in the brain monitors blood flow through the brain.
  • The temperature sensors in the skin send impulse signals to the thermoregulatory centre about random temperature changes.

Two ways your body tries to cool down are to make you flush when blood rushes to your skin making you go red as heat tries to escape or by sweating. Sweat (water and salt) oozes out of your sweat glands. This then evaporates and as it does it cools the skin.

Three ways in which your body warms you up are: blood vessels which supply skin capillaries close up to reduce blood flow. You look pale as less blood is close to the surface of your skin. You shiver as your muscles contract and relax rapidly, causing lots of cellular respiration and generates heat, and sweat production is reduced.

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Water Regulation


  • You get thirsty.
  • May feel dizzy.
  • Suffer from concentrated urine.

Over Intake:

  • Kidneys excrete excess water.
  • Urine is pale and diluted.
  • Anti-diuretic.

Too much water dilutes the blood. The hypothalamus sense this and induce the release of ADH (Anti Diuretic Hormones).

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Controlling Blood Sugar

Hormones are secreted by the pancreas and control the blood sugar sugar level in your blood.

Insulin is a hormone used by the pancreas to control the glucose concentration in your blood.

Diabetes is when you produce little or no insulin allowing your blood sugar levels to increase. Your kidneys then begin to produce glucose in urine and you urinate a lot. No glucose gets to your cells so you feel tired and lose weight as you break down fat and protein instead.

Glycogen is an insoluble carbohydrate stored in your liver.

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Controlling Blood Sugar Continued

  • When your blood sugar levels become too high, insulin is released by the pancreas. It causes your liver to get rid of any extra glucose in your blood. The soluble glucose gets converted into glycogen, which is insoluble. However, when the concentration of glucose in your blood falls, the pancreas secretes glucagon.
  • It is impotant to control the level of glucose in your blood because without enough, you wouldn't be able to respire.
  • If you have mild diabetes, avoiding carbohydrate-rich foods will help. With more severe cases insulin is injected into the stomach to make up for the lack of it. This does NOT cure it, it only treats it. It is injected so it goes straight into the bloodstream.
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DNA stands for deoxyribose nucleic acid and are the long molecules which make up chromosomes.

Cells are the basic building blocks of a living organism.

Genes are small packets of information that contain caracteristics.

Chromosmes are thread like structures holding genes.

Nucleus is the part of the cell that contains genetic information.

Size order (smallest to biggest): DNA, Gene, Chromosome, Nucleus, Cell.

  • One pair of chromosomes are the same which means they are homolygous.
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Inheritance Continued

Inheritance or Heredity is the genetic translation of characteristics from parent to offspring, such as, hair, eye and skin colour.

Homologous Chromosomes is a pair of matching chromosomes in an organism, with one being inherited from each parent.

Autosome is a chromosome that is not a sex chromosome.

Genotypes are the genes present in the DNA of an organism. There are always two letters in the genotype:

1 from mum + 1 from dad = 2 genes (2 letters) for offspring.

Three possible genotypes are: 1. 2 capital letters, for example, TT. 2. 1 of each, such as Tt and 3. 2 lower case letters, e.g tt.

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Inheritance Continued

Homozygous is a genotype that has 2 capital letters or 2 lower case letters. They are the SAME. Sometimes the term purebred is used instead of homozygous.

Heterozygous is a genotype that has 1 capital letter and 1 lower case letter. Hetero means "other" and so they are DIFFERENT. A heterozygous genotype can also be referred to as hybrid.

Phenotype is how the trait physically shows up in the organism; it is what the organism looks like. Examples are: blue eyes, brown fur, striped fruit, yellow flowers etc.

Alleles are alternative forms of the same gene. Alleles for a trait are located at corresponding positions on homologous chromosomes called loci.

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Inheritance Continued

If we were to cross red flowers with white flowers and ended up with red flowers, it would mean that the red gene is DOMINANT and the white is RECCESSIVE. The letter for the red allele would be R (capital) and the letter for the white allele would be r (lower case). The phenotypes are red and white and homozygous flowers would be represented as: RR (2 capital) for red flowers and rr (2 lower case for white flowers.

If we were to cross two homozygous flowers, one white and one red we would still get red flowers as each offspring would have a dominant gene.

If we were to cross two heterozygous flowers,both with the genotypes Rr (1 capital and 1 lower case) , the ratio of red flowers:white flowers would be 3:1.

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Cell Division-Mitosis

  • DOESN'T happen in sex cells but in all other cells.
  • The product of mitosis is two indentical.

Stage 1. Copy all chromosomes.

Stage 2. Cell membrane breaks down and a spindle forms.

Stage 3. All of the chromosomes line up at the middle of the spindle.

Stage 4. Chromosomes split at centromeres and go to the poles of the spindle.

Stage 5. The two nuclear membranes form around the chromosome and spindle breaks down.

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Cell Division-Meiosis

  • Meiosis takes place in sex cells (gametes).
  • There are 23 pairs of chromosomes in a normal human body cell (46 in total).
  • There are 23 chromosomes in a human egg cell.
  • Ther are 46 chromosomes in a fertilised human egg cell.

In sexual reproduction, the gametes are produced by meiosis in the sex organs of the parents which means that each gamete is different. When the gametes fuse there is one of each pair of chromosomes and so one of each pair of genes comes from each parent. The combination of genes in the new pair will contain alleles (different forms of the gene from each parent). This also produces different characteristics in the offspring.

During meiosis, the number of chromosomes is reduced by half. The chromosomes are first copied so there are four sets of chromosomes. Then, the cell divides twice in quick succession to form four gametes, each with a single set of chromosomes.

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Stem Cells

  • Stem cells are unspecialised which means they don't have a specific job.
  • They can be made into any type of cell and given any job.
  • They are found in blood cells in your bone marrow.
  • There are two types of stem cell:

1. Adult

2. Embyonic either directly from an embryo or from the umbilical cord.

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