There Are Six Areas Within Biology That You Will Be Tested on in January

Revision

There are six areas within biology that you will be tested on in January:

Cells

How do plants produce food?

Energy flows

Enzymes

Homeostasis

Inheritance

The following is a brief overview of these areas to help you with your revision. This is only a supplementto the revision you are doing, and should not be used as a substitute!

Good luck in the exam! 

Cells

What you should know:

Animal and plant cells contain a nucleus, cell membrane, cytoplasm, mitochondria and ribosomes.

The functions of these organelles (parts of the cell).

Plant cells also have a cell wall, chloroplasts and a permanent vacuole.

The functions of these organelles (parts of the cell).

Some cells are specialised to carry out their function, e.g. sperm, cone, red blood and fat cells in animals and root hair and palisade cells in plants.

How the above examples are adapted to their functions

Dissolved substances move in and out of cells by osmosis and diffusion (and active transport).

How the processes of diffusion are similar and how they are different.

Diffusion is the net movement of particles from a HIGH concentration to a low concentration.

Osmosis is the net movement of water from a HIGH water concentration (dilute solution) to a low water concentration (concentrated solution), through a partially permeable membrane.

Quick questions on cells:

1. Name three structures found in both plant AND animal cells

1. Where does aerobic respiration take place?

1. Name two specialised cells and describe how they are adapted for their function

1. What do we call the process where cells become specialised?

1. Name two substances that diffuse out of cells

1. Which of the following requires energy to happen:
2. osmosis
3. diffusion
4. active transport
5. Name an adaptation some cells have for faster diffusion

How Do Plants Produce Food?

What you should know:

Photosynthesis can only be carried out by green plants, as they contain a substance called chlorophyll which traps the Sun’s energy.

How leaves are well adapted to allow the maximum photosynthesis to take place.

The equation for photosynthesis.

Glucose is produced in photosynthesis and is used for respiration.

Glucose is stored as insoluble starch so it has no effect on osmosis.

Glucose is also combined with other nutrients (mineral ions) by the plant to produce new materials.

Sugars are transported by the phloem, and water and mineral ions are carried by the xylem. Phloem and xylem together with cambium cells between them are called a vascular bundle.

How you can test for products of photosynthesis (using iodine to test for starch and a glowing splint relights in the presence of oxygen).

There are three main factors that limit the rate of photosynthesis (limiting factors)

• Light intensity (arbitrary units)
• Temperature (°c) (linked to enzymes, optimum temp)
• Carbon dioxide concentration (%)

To be able to interpret graphs of these limiting factors

We can artificially change the environment in which we grow plants. We can use this to observe the effects of different factors on the rate of photosynthesis, and also control the rates of photosynthesis.

Plants need other substances to grow, and absorb these through their roots. If a plant is deficient in these mineral ions, it develops symptoms because it cannot grow properly.

• Nitrates are needed for making proteins (stunted growth)
• Magnesium is needed to make chlorophyll (yellow leaves)

Quick questions on plants:

1. What is the word equation for photosynthesis?

1. Where does the energy for photosynthesis come from?

1. Why is the waste product of photosynthesis so important? How could you test for this substance?

1. Why does photosynthesis slow down on a cold day?

1. Why would there be little point in heating a greenhouse on a hot day?

1. How is glucose stored? Why?

1. What is meant by ‘respiration’?

1. How do plants take minerals from the soil?

1. What does ‘deficiency’ mean?

1. If crops are grown for long periods of time on the same land, they may use up some of the minerals in the soil. State two ways in which farmers can avoid these crops dying from lack of minerals.

Energy Flows

What you should know:

Radiation from the Sun is the main source of energy for all living things. The Sun’s energy is captured and used by plants during photosynthesis.

All food chains start with a producer (green plant), followed by a herbivore or omnivore then usually a carnivore.

Biomass is the mass of living material in a plant or animal. Pyramids of biomass represent the mass of all the organisms at each stage in a food chain. Producers (green plants) are always at the BOTTOM!!!

Pyramids of number are not always pyramid-shaped!

A pyramid of biomass is likely to give a more accurate picture than a pyramid of numbers.

Pyramids of biomass are pyramid-shaped! This is because biomass decreases at each trophic level (stage) for the following reasons:

• Not all organisms at one stage are eaten by the stage above
• Some material taken in by the organism is excreted
• Some of it is used in respiration

Energy is lost between trophic levels to the environment by

• Excretion
• Movement
• Undigested food
• Maintaining body temperature

You should be able to interpret Sankey Diagrams, which show how energy is lost from an organism. The bigger the arrow, the more energy is lost that way.

Herbivores lose the most amount of energy through undigested food.

Carnivores lose the most amount of energy through movement (hunting for prey).

Warm-blooded animals lose the most amount of energy through heat production (keeping their body temperature constant).

Cold-blooded animals have little energy loss through heat production, as they take on the temperature of the surrounding environment.

The efficiency of food production can be improved by reducing the amount of stages in a food chain. It would be most efficient if we were all vegetarians!

We can artificially produce meat more efficiently by:

• Restricting the animals movement, so energy is not lost this way
• Controlling the surrounding temperature, so the animal doesn’t use energy from food keeping itself warm.

However, this is controversial and people think it is cruel.

Minerals and nutrients are constantly recycled and returned to the environment.

A group of micro-organisms called decomposers help this process of decay, they include bacteria and fungi.

Detritus feeders (maggots and worms) start the decay process by breaking down the dead organism and produce waste materials.

Decomposers then digest everything!

Decomposers release carbon dioxide, water and minerals which plants can use.

Decay occurs quicker when it is warm (enzymes) and wet (dissolve food, prevent from drying out), with a good supply of oxygen (for respiration).

In a stable community the processes that remove materials are balances by the processes which return materials.

The energy originally captured by green plants is eventually transferred back into plants, into decomposers or as heat into the environment.

We use decomposers in sewage treatment plants to break down our bodily waste – nice!

We also use decomposers in compost heaps, to gradually break down vegetable peelings, grass cuttings etc, then use it as fertiliser.

Carbon is constantly cycled in nature: this is known as the carbon cycle.

There are three main processes in the carbon cycle

• Photosynthesis
• Respiration
• Combustion

Learn the equations for each of the three processes above and how each adds/removes carbon from the atmosphere.

How humans are adding excess carbon to the cycle (deforestation and burning fossil fuels).

Quick Questions on Energy Flows:

1. Why is energy lost between the different stages of a food chain?

1. What is meant by the term ‘biomass’?

1. Why does a running horse need more energy than one eating grass in a field?

1. Why do we say in terms of food production, that meat is ‘expensive’ to produce?

1. How can you limit energy losses in a food chain?

1. Which organisms break down dead and waste material?

1. Why is decay faster when it is warm?

1. Which process results in carbon dioxide being taken out of the atmosphere?

1. When do plants respire?

Enzymes

What you should know:

The definitions of

• Enzyme
• Catalyst
• Substrate
• Active site
• Activation energy
• Enzyme-substrate complex

Enzymes are protein molecules made up of long, folded chains of amino acids. This makes them specific (a certain shape), so only a certain substrate can bind (fit) into the active site, to produce a product.

Hydrogen peroxide (toxic) is broken down into oxygen and water (two non-toxic products) by catalase, an enzyme, in the liver.

Enzymes are important as they catalyse reactions such as respiration, photosynthesis and protein synthesis in living cells.

Temperature and pH are two factors which effect enzyme action.

• Too hot (usually above 40°c) and the enzyme is denatured, the active site is changed, so the substrate can no longer bind and release a product
• Incorrect pH and the forces holding the enzyme together are affected, again denaturing the enzyme by changing the active site.

The word equation for aerobic respiration

To know that aerobic means with oxygen, and anaerobic means without oxygen.

Respiration takes place in an organelle called a mitochondria.

Respiration is important because:

• It releases energy from food so cells of body can use it
• Building up large molecules from smaller ones (synthesis) in animals and plants
• Making muscles contract in animals
• Maintaining body temperature in warm-blooded animals (birds and mammals)

Enzymes catalyse the breakdown of large food molecules into smaller molecules during digestion.

Digestive enzymes are produced inside cells but they work outside cells in the gut.

Enzymes are produced in organelles called ribosomes, as enzymes are proteins and ribosomes are the site of protein synthesis.

Carbohydrase (amylase) breaks down carbohydrates into simple sugars, which are then used in respiration. It is produced in the salivary glands, pancreas and small intestine.

Protease breaks down proteins into amino acids, which are then used for protein synthesis. It is made by the stomach, pancreas and small intestine.

• Pepsin is a protease made by the stomach. It works best at around pH2. Therefore, hydrochloric (stomach) acid is produced to create the acidic, optimum conditions.
• Trypsin is a protease made by the small intestine. It works best at around pH8. Therefore, bile is squirted into the small intestine to neutralise the food/stomach acid and create the alkaline, optimum conditions.

Lipase breaks down fats (lipids) into fatty acids and glycerol, which are then used as a source of energy, to build cell membranes, nake hormones or fat stores. It is made by pancreas and small intestine.

Remember, no digestion occurs in the pancreas, so any enzymes made here go to the small intestine.

Once your food has been digested by these enzymes, the soluble molecules produced leave your small intestineand pass into your blood supply to be carried to the cells which need them.

Bile neutralises the food make acidic from the stomach entering the small intestine and also emulsifies fats (breaks large drops into smaller ones) to provide a larger surface area for the enzymes to work on. Remember bile is NOT an enzyme and it doesn’t break down fats!

Bile is produced by the liver and stored in the gall bladder.

.Enzymes are used in industry:

• Protease is used in baby food to pre-digest proteins
• Isomerase is used to convert glucose into fructose in slimming foods
• Carbohydrase is used to convert starch into sugar (glucose) syrup.

Enzymes catalyse many normally expensive processes at low temperatures and normal pressures, making it cheaper.

However, carefully controlling temperature and pHfor these reactionscosts money.

Quick Questions on Enzymes:

1. What type of molecules are enzymes?

1. What does ‘catalysis’ mean?

1. Why does an increase in temperature initially increase the rate of reaction?

1. Why do enzymes stop working if the temperature gets too hot?

1. What is needed for muscles to contract?

1. What are amino acids built up into?

1. Which enzymes does the pancreas produce?

1. What conditions are best for the small intestine? How is this achieved?

1. Why is fructose used in slimming foods?

1. Where is bile made and where is it stored?

1. Why would you not use a temperature above 45°c if you are using a biological washing powder?

Homeostasis

What you should know:

The internal conditions of your body have to be controlled to maintain a constant internal state.

Homeo = same, stasis = state

Poisonous waste products are made all the time in the body through chemical reactions and need to be removed.

E.g. carbon dioxide, produced during cellular respiration in the mitochondria, is removed by the lungs when you exhale.

Also, urea produced by the liver when excess amino acids are broken down, is firstly filtered out of your blood by your kidneys and is combined with water and ions to form urine, which is stored in your bladder until it leaves your body through the process of urination.

Remember: urea is produced by the liver and excreted by the kidneys!

The water and ion content of cells also needs to be maintained. If not, then too little or too much water may move in and out of cells by osmosis.

Body temperature must also be controlled and maintained at the level which enzymes work best (optimum = 37.5°c). A few degrees above/below means the enzymes cannot function properly, you wont make enough energy and your cells begin to die… nice!

The thermoregulatory centre of the brain and receptors in the skin detect changes in temperature.

The thermoregulatory centre controls the bodys response to a change in internal temperature.

Too cold:

• Blood vessels near surface of the skin constrict allowing less blood to flow through the capillaries, so less heat is lost by radiation
• Sweat production is reduced
• Shivering begins due to muscles contracting quickly, which releases heat energy from cellular respiration.
• Goosebumps are formed when hairs are pulled up to trap an insulating layer of air

Too hot:

• Blood vessels near surface of the skin dilate allowing more blood to flow through the capillaries, and more heat is lost by radiation
• Sweat glands produce sweat, helping the body to cool down by evaporationby taking energy away from the skin.

Blood glucose concentration must be kept at the correct level. It is monitored and controlled by your pancreas which releases two hormones, insulin and glucagon.

Too little glucose:

• Glucagon produced (remember: where has all the glucose gone?!)
• Makes liver break down glycogen back into glucose

Too much glucose:

• Insulin produced (there is an INcrease!)
• Excess sugar stored as insoluble glycogen in liver

In diabetes, the pancreas does not produce enough insulin so the blood glucose level may rose fatally. It can be treated by insulin injectionsso the hormone is delivered directly to the blood, and avoiding carbohydrate-rich foods. An alternative is transplantation, but there are not enough dead donors and a living donor could experience the risks of surgery.

Banting and Best invstigated diabetes by experimenting on dogs. Some were made diabetic by removing their pancreas, and extracting insulin from the pancreases of other dogs.

Ethically, this was seen by some as cruel, as many dogs died during the experiments.

However, the scientists did find a way of treating diabetes and for many years insulin from pigs and cows was used to treat diabetics.

You should be able to evaluate experimental data from Banting and Best’s experiments which led to insulin being discovered.

Human insulin is now mass produced using genetic engineering. Bacterial DNA are inserted with the gene for insulin and divide rapidly, producing a lot of insulin.

Stem cells could be used to create new functioning pancreas cells which make their own insulin, but again ethics are involved as the embryos are created specifically for this purpose.

Quick Questions on Homeostasis:

1. What happens to the amino acids that we don’t use?

1. Where is urea produced?

1. Why is controlling the water an ion content of the body important?

1. Which two areas in the body detect temperature change?

1. Why does sweating cool us down?

1. What effect does shivering have on the body?

1. Which two hormones control blood glucose level? Where are they produced?

1. What happens to blood vessels when you are cold? And when you are hot?

1. Give an advantage of using genetically engineered insulin rather than an injection.

Inheritance