BIOLOGY T3 & T4

Question 1

What is a hormone?

Answer 1

A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.

Question 2

What are the four endocrine glands?

Answer 2

There are many endocrine glands in the human body, you need to know the following:

• Adrenal glands
• Pancreas
• Testes
• Ovaries

Question 3

Describe the adrenal glands.

Answer 3

The adrenal glands:

• Are attached to the back of each kidney
• Produce the hormone adrenaline (sometimes called epinephrine).

Question 4

What is the effect of adrenaline?

Answer 4

In response to a stressful situation nerve impulses are sent to the adrenal medulla, causing it to release adrenaline into the bloodstream.
When adrenaline is released into the blood stream by the adrenal glands, it causes a “fight or flight” response.
- The breathing rate increases, becoming faster and deeper.
- The heart rate increases, increasing the pulse rate.
- The pupils dilate, allowing more light into the eye.

Question 5

What are some other effects of adrenaline?

Answer 5

• The liver is stimulated to convert glycogen to glucose. This makes more glucose available in the blood for energy production, allowing metabolic activity to increase.
• Skeletal muscles tense so they can respond quicker.
• Muscles in the alimentary canal relax, peristalsis and digestion slow down; more energy is available.
• Arterioles in the skin contract, providing more blood for muscles - this makes the person look pale.

Question 6

Describe the pancreas.

Answer 6

The pancreas is a digestive gland that secretes enzymes into the duodenum (first part of the small intestine.
These enzymes are:
- Pancreatic proteases that digest protein (Trypsin).
- Pancreatic amylase that digests carbohydrates.
- Pancreatic lipase that digests lipids.
It also produces the hormones insulin and glucagon that regulate the blood glucose levels.

Question 7

What happens if blood glucose levels are too low?

Answer 7

The hormone producing cells of the pancreas are arranged in small groups called islets.
If blood glucose falls, the islets release a hormone called glucagon into the bloodstream.
Glucagon acts on cells in the liver causing them to convert stored glycogen back into glucose, this brings levels back up.

Question 8

What happens if blood glucose levels are too high?

Answer 8

Insulin has the opposite effect to glucagon.
If the blood glucose level increases (e.g. after a carbohydrate rich meal), insulin is released causing the liver to take glucose out of the blood and store it as glycogen.

Question 9

Which hormone do the ovaries produce and what is its function?

Answer 9

The ovaries produce oestrogen which prepare the uterus for the implantation of the embryo by making its lining thicker and increasing the blood supply.

Question 10

Which hormone do the testes produce and what is its function?

Answer 10

The testes produce testosterone which plays a role in developing the secondary sexual characteristics in males.

Question 11

What are the differences between the endocrine and nervous control systems?

Answer 11

• Endocrine involves the transmission of chemicals whereas nervous involves the transmission of electrical impulses.
• Endocrine the transmission occurs via the blood whereas in nervous it is transmitted in nerves.
• Endocrine is a slow transmission whereas nervous is a rapid transmission.
• Endocrine the hormones are dispersed throughout the body whereas for nervous the impulse is sent directly to the target organ.
• Endocrine there are long-term effects whereas for nervous there are short-term effects.

Question 12

What is homeostasis?

Answer 12

Homeostasis is the maintenance of a constant internal environment.

Question 13

What is the purpose of homeostasis?

Answer 13

The internal environment needs to be kept relatively constant to allow important biological reactions to occur.
This maintenance also keeps the conditions in the tissue fluid around cells constant.

Question 14

What are the set limits of homeostasis?

Answer 14

• The body’s temperature is kept at around 37 degrees.
• The pH of the blood is kept constant by removing the build up of carbon dioxide.
• The water and salt content of the blood is regulated by the kidneys.
• Blood sugar is regulated by the liver and pancreas.

Question 15

What is a negative feedback loop?

Answer 15

When conditions move outside of the set limits, the change is detected by receptors in the body.
This triggers a response in other parts of the body to counteract that change and bring it back within set limits.

Question 16

What happens when the body is too hot?

Answer 16

• More blood flows near the surface of the skin allowing more heat to be exchanged with the surroundings (vasodilation).
• Sweat glands secrete sweat onto the skins surface, when it evaporates it takes heat away from the body.

Question 17

What happens when the body is too cold?

Answer 17

• Less blood flows near the surface of the skin (shunt vessels), reducing the heat loss to the surroundings (vasoconstriction).
• Sweat production stops.
• Shivering occurs - uncontrollable, rapid bursts of muscular constrictions to release heat.

Question 18

What are tropic responses?

Answer 18

A plants response to a stimulus is referred to as a tropic response. The response can be positive: towards, or negative: away from the stimulus.

Question 19

What is gravitropism?

Answer 19

Gravitropism is a response where a plant grows towards or away from gravity. The roots of a plant are positively gravitropic and grow towards gravity, the shoots of plants are negatively gravitropic and grow away from the direction of gravity.

Question 20

What is phototropism?

Answer 20

Phototropism is a response where a plant grows towards or away from the direction light is coming from.
The shoots of plants are positively phototropic and grow towards the light, while the roots are negatively phototropic and grow away from the light.

Question 21

What is auxin?

Answer 21

Phototropism and gravitropism responses are controlled by the plant hormone auxin.
Auxin is produced in the growing tips of shoots and roots, its effect is different in both.

Question 22

Describe auxin’s role in phototropism.

Answer 22

In phototropism:

• Auxin causes elongation of shoot cells on the shaded side of the plant.
• The elongation on the shaded side causes the shoot to bend towards the direction of the light source.
• If a shoot is placed horizontally the auxin will accumulate on the lower side (it moves down due to gravity).
• This causes the lower side to elongate and grow faster, making the shoot grow upwards.

Question 23

Describe auxin’s role in gravitropism.

Answer 23

• Auxin inhibits the growth of root cells.
• It accumulates in the lower part of roots due to gravity.
• It slows the growth of the lower side of the roots, the upper side grows faster and the root grows down.

Question 24

What is inheritance?

Answer 24

Inheritance is the transmission of genetic information from generation to generation.

Question 25

What is a chromosome?

Answer 25

A chromosome is a thread-like structure of DNA, carrying genetic information in the form of genes.
They are found in the nucleus of cells.
Chromosomes come in homologous pairs, one from the mother and one from the father.
This means that you have two copies of each chromosome, which means you have two copies of each gene.

Question 26

What is a gene?

Answer 26

A gene is a length of DNA coding for a protein.

Genes are part of the DNA that code for physical traits e.g. hair or eye colour.

Question 27

What is an allele?

Answer 27

An allele is the alternative version of a gene.
Alleles can be dominant or recessive.
Dominant alleles always take precedence over recessive alleles.
E.g. the gene for brown eyes is dominant and the gene for blue eyes is recessive. This means that if your mother passed on the gene for blue eyes and your father passed on the gene for brown eyes, you would have brown eyes.

Question 28

What is mitosis?

Answer 28

Mitosis is the process when one somatic (body) cell divides into two identical copies.
Everything inside the cell (including the organelles and chromosomes) are doubled and the cell divides.

Question 29

What is the purpose of mitosis?

Answer 29

The main three purposes of mitosis are:

• Growth, and the repair of damaged tissues.
• Replacement of cells.
• Asexual reproduction.

Question 30

What is the difference between haploid and diploid nuclei?

Answer 30

A haploid nucleus contains a single set of unpaired chromosomes (in gametes) whereas a diploid nucleus contains two sets of chromosomes (in body cells).

Question 31

What is meiosis?

Answer 31

Meiosis is nuclear division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells.

Question 32

What is the purpose of meiosis?

Answer 32

Meiosis is involved in the production of gametes which ensures variation by forming new combinations of maternal and paternal chromosomes. This variation is required for survival in a species.

Question 33

What are the two stages of protein synthesis?

Answer 33

Transcription and translation.

Question 34

What occurs during transcription?

Answer 34

RNA polymerase attaches to the DNA using the base-pairing rules and transcribes a single strand (the template strand), forming mRNA (messenger RNA).
When RNA polymerase transcribes the DNA uracil (U) binds to adenine, rather than thymine.
RNA polymerase releases the mRNA polymer and detaches from the DNA - the DNA recoils.

Question 35

What occurs during translation?

Answer 35

The mRNA leaves the nucleus via the nuclear pore and it attaches to a ribosome.
The ribosome “reads” the mRNA in sequences of three (codons).
tRNA (transfer RNA) attaches to the amino acids found in the cytoplasm using the three bases on the end of the tRNA. The bases on the tRNA are anti-codons.
These anti-codons are complementary to the codons and so the tRNA attaches to the mRNA and the anti-codons and codons combine to form an amino acid.
In the ribosome these amino acids then bond to eachother with peptide bonds, forming a polypeptide chain.
Once the whole strand has been translated, the polypeptide chain forms a protein.

Question 36

What is the genotype?

Answer 36

The genotype is the genetic make-up of an organism in terms of the alleles present.

Question 37

What is the phenotype?

Answer 37

The phenotype is the observable features of an organism.

Question 38

What is homozygous?

Answer 38

Homozygous is having two identical alleles of a particular gene. Two identical homozygous individuals that breed together will be pure-breeding.

Question 39

What is heterozygous?

Answer 39

Heterozygous is having two different alleles of a particular gene. A heterozygous individual will not be pure-breeding.

Question 40

What is the difference between a dominant and a recessive allele?

Answer 40

A dominant allele is one that is expressed if it is present whereas a recessive allele is only expressed when there is no dominant allele of the genes present.

Question 41

What is variation?

Answer 41

It is the differences between individuals of the same species.

Question 42

What is the difference between continuous and discontinuous variation?

Answer 42

Continuous variation is a characteristic that can have any value in a range e.g. height in humans, whereas discontinuous variation is a characteristic that can be one of a certain number of alternatives (either/or) e.g. tongue rolling.

Question 43

What is a mutation?

Answer 43

A mutation is a random and spontaneous change in the DNA sequence. Mutations are caused by mutations. New alleles are formed by mutations.

Question 44

What is a gene mutation?

Answer 44

A gene mutation is a change in the base sequence of DNA.

Question 45

What are the symptoms of sickle cell anaemia?

Answer 45

The sickle cell mutation causes red blood cells to become sickle shaped. This reduces the ability of the individual to carry oxygen. This is very dangerous in the homozygous condition and leads to early death.
People heterozygous for sickle cell anaemia have an advantage in malaria affected countries. The sickle cell mutation makes these individuals resistant to malaria.

Question 46

What is phenotypic variation caused by?

Answer 46

Phenotypic variation is caused by both environmental variation (acquired characteristics) and genetic variation (inherited characteristics).

Question 47

What is environmental variation?

Answer 47

Environmental variation (acquired characteristics) can be caused by things like diet, climate, culture and lifestyle. E.g. sun tan, hair style, weight.

Question 48

What is genetic variation?

Answer 48

Genetic variation (inherited characteristics) can be brought about by genes. These include things like hair or eye colour.

Question 49

What is the difference between a somatic and germ-line mutation?

Answer 49

Somatic mutations occur in a single body cell and cannot be inherited - only tissues derived from the mutated cell are affected. Germ-line mutation occur in gametes and can be passed onto offspring - every cell in the entire organism will be affected.

Question 50

What is an adaptive feature?

Answer 50

Adaptive features are the inherited functional features of an organism that increase its fitness. Fitness is the probability of an organism surviving and reproducing in the environment in which it is found.

Question 51

What are the requirements for natural selection?

Answer 51

1. Variation within populations
2. Overproduction of offspring
3. Competition for resources
4. Struggle for survival
5. Reproduction by individuals that are better adapted to the environment than others
6. The fittest passing on of their alleles to the next generation

Question 52

What is selective breeding?

Answer 52

This is selection by humans of individuals with desirable features and then crossing these individuals to produce the next generation. Then the same selection occurs with the offspring which shows the same desirable features.

Question 53

What is evolution?

Answer 53

Evolution is the change in adaptive features of a population over time as the result of natural selection.

Question 54

What is adaptation?

Answer 54

Adaptation is the process, resulting from natural selection, by which populations become more suited to their environment over many generations.

Question 55

Why are bacteria often used in biotechnology and genetic engineering?

Answer 55

They are used due to”

• Their rapid reproduction rate
• Their ability to make complex molecules
• The lack of ethical concerns over their manipulation and growth
• The presence of plasmids
• They have DNA and a genetic code like all other living organisms

Question 56

What is genetic engineering?

Answer 56

Genetic engineering is the process of changing the genetic material of an organism by removing, changing, or inserting individual genes from different species.

Question 57

What are the different types of antibiotic?

Answer 57

Those which stop the bacteria from reproducing are called bacteriostatic antibiotics, and those which kill the bacteria are called bacteriocidal.

Question 58

What does pectinases do?

Answer 58

Pectinases are used to separate the juices from fruit such as apples. They break down pectin, the jelly-like substance that sticks plant cell walls to each other. The enzymes can also be used to clarify fruit juice and wine. The sugars produced also make the juice sweeter.

Question 59

How is bread made?

Answer 59

Flour, water, salt, oil and yeast are mixed to make the dough. The addition of water activates the amylases in the flour which digest some of the starch to sugar. The yeast then ferments the sugar to alcohol and carbon dioxide. A protein called gluten gives the dough a sticky, plastic texture which holds the bubbles of gas. After leaving the dough at a temperature of 27 degrees for an hour or two, the dough can then be baked and the temperature makes the bubbles expand more, kills the yeast, and evaporates the small quantities of alcohol.

Question 60

How are enzymes used in biological washing powders?

Answer 60

Proteases (protein-digesting enzymes) and lipases (fat-digesting enzymes) are used in washing powders as they are effective in removing stains in clothes e.g. form blood, egg, grease etc. When they have been digested the products are small, soluble molecules which can pass out of the cloth. These washing powders save energy as they can be used to wash clothes at lower temperatures. However the enzymes become denatured at high temperatures.

Question 61

How is lactose-free milk produced?

Answer 61

The simple way is to add lactase to the milk. The enzyme breaks down lactose sugar into two monosaccharide sugars: glucose and galactose. Both can be absorbed by the intestine so are not a problem for lactose intolerant people.

Question 62

How is the antibiotic penicillin produced?

Answer 62

Penicillin is produced by mutant forms of a species of the fungus, penicillium. Antibiotics are produced in giant fermentation tanks, up to 100,000 litres capacity. These tanks are filled with a nutrient solution. Mineral salts are added, the pH is adjusted to between 5 and 6, the temperature is maintained at about 26 degrees and oxygen is blown through the liquid and it is stirred. The nutrient liquid is filtered by a culture of the appropriate micro-organism which is allowed to grow for a day or two. As the nutrient supply diminishes, the micro-organisms secrete their antibiotics and the nutrient fluid containing the antibiotic is filtered off.

Question 63

How is insulin produced using bacteria?

Answer 63

The human insulin gene is inserted into bacteria, which then secrete human insulin. The human insulin produced this way is purer than insulin prepared from pigs or cattle, which sometimes provokes allergic reactions owing to traces of ‘foreign’ protein. The GM insulin is acceptable to people with a range of religious beliefs who may not be allowed to use insulin from cows or pigs.

Question 64

How is bacteria used in genetic engineering?

Answer 64

1. Restriction enzymes are used to isolate the DNA making up a human gene, forming sticky ends.
2. The same restriction enzymes are used to cut the bacterial plasmid DNA, forming complementary sticky ends.
3. The human DNA is inserted into the bacterial plasmid DNA using DNA ligase to form a recombinant plasmid.
4. The plasmid is then inserted back into the bacteria where it can reproduce.

Question 65

How is genetic engineering used to make crop plants resistant to herbicides?

Answer 65

Some of the safest and most effective herbicides such as glyphosate kill any green plant but become harmless as soon as they reach the soil. These herbicides cannot be used on crops because they kill the crop plants as well as the weeds. A gene for an enzyme that breaks down glyphosate can be introduced into a plant cell culture to make it resistant to these herbicides.

Question 66

How is genetic engineering used to make crop plants resistant to insect pests?

Answer 66

A gene from a bacterium that produces a toxin that kills caterpillars and other insect larvae has been successfully introduced into some plant species. The plants produce the toxin and show increased resistance to attack by insect larvae. The gene is also passed on to the plant’s offspring. However, there are signs that insects are developing immunity to this toxin.

Question 67

How has modern technology increased food production?

Answer 67

• Agricultural machinery is used for larger areas of land and to improve efficiency
• Chemical fertilisers are used to improve yields
• Insecticides are used to improve quality and yield
• Herbicides are used to reduce competition with weeds
• Selective breeding is used to improve production by crop plants and livestock e.g. cattle, fish and poultry

Question 68

What are the impacts of monocultures?

Answer 68

In a monoculture, any organisms that feed on, compete with or infect the crop plant are destroyed. So the balanced life of a natural plant and animal community is displaced from farmland and left to survive only in small areas of woodland, heath or hedgerow.

Question 69

What are the impacts of intensive livestock production?

Answer 69

Intensive livestock production or factory farming is when chickens and calves are often reared in large sheds instead of open fields. Their urine and faeces are washed out of the sheds with water forming slurry. If this slurry gets into streams and rivers it supplies an excess of nitrates and phosphates for the microscopic algae. This can lead to eutrophication. Over grazing of livestock can also lead to erosion.

Question 70

What is eutrophication?

Answer 70

• When nitrates and phosphates enter the water, they become available for algae
• Algae (like all plants) use these nutrients to grow, and more nutrients means faster growth
• As the algae grows, some of it gets blocked off from the light due to overcrowding
• The algae, and other aquatic plants, without light die and aerobic bacteria decompose them and respire
• This removes oxygen from the environment and adds more carbon dioxide
• The oxygen levels drop and marine animals suffocate, this can collapse the ecosystem

Question 71

What are the causes of famine?

Answer 71

1. Reasons for unequal distribution of food e.g. war
2. Drought
3. Flooding
4. Increasing population
5. Poverty

Question 72

What are some reasons for habitat destruction?

Answer 72

1. Increased area for food crop growth, livestock production and housing
2. Extraction of natural resources
3. Marine pollution

Question 73

What are the negative effects of deforestation?

Answer 73

Trees can grow on hillsides even when the soil layer is quite thin. When the trees are cut down and the soil ploughed, there is less protection from the wind and rain. Heavy rainfall washes the soil off the hillsides into the rivers. The hillsides are left bare and useless and the rivers become choked up with mud and silt, which can cause floods. It can also result in the loss of thousands of species of animals and plants forever. Removal of trees on such a large scale also reduces the amount of carbon dioxide removed from the atmosphere through photosynthesis.

Question 74

How do insecticides pollute the environment?

Answer 74

Some of the insecticides used remain the environment for a long time. DDT was used to control the spread of malaria by killing mosquitoes. It is absorbed at sub-lethal doses by micro-organisms and can increase as it passes through a food chain..
DDT also caused birds to lay eggs with very thin shells, they broke easily so fewer chicks were raised.

Question 75

How do herbicides pollute the environment?

Answer 75

Herbicides have similar issues as pesticides, if they don’t break down they can disrupt the environment. If herbicides leach from farmland into waterways they can kill aquatic plants, herbivores lose their food source and starve or migrate, carnivores that eat the herbivores are affected as well.

Question 76

How does a nuclear fall-out pollute the environment?

Answer 76

This could be the result of a leak from a nuclear power station, or from an explosive. Radioactive materials are carried by the wind and water and settle into an environment. The half-life of these materials can be very long, this means the radiation can stay around for many years. It can cause cancer in the living organisms which absorb the radiation.

Question 77

How does chemical waste pollute the environment?

Answer 77

Many industrial processes produce poisonous waste products. If these waste products are released into the environment they will poison plants, animals, and people that live in the area. These poisons can accumulate in the tissues of plants and animals in the same way as the herbicides and pesticides.

Question 78

How does discarded rubbish pollute the environment?

Answer 78

The development of towns and cities, and increased numbers of people in one place, leads to problems with waste disposal. The accumulation of waste in landfills can pollute the area, sometimes waste is burned which adds to air pollution. The waste can attract undesirable animals like rats, which can spread disease. A lot of the rubbish ends up in the sea where it causes severe problems for marine life.

Question 79

How does sewage pollute the environment?

Answer 79

Diseases like cholera and typhoid are caused by certain bacteria when they get into the intestines. People suffering from these illnesses pass bacteria in their faeces. If sewage is not treated properly, many people can get infected. The sewage is treated and broken down, removing the harmful bacteria and their toxins. The products left over are high in nitrates and phosphates, these can cause rapid algal growth and contribute to eutrophication.

Question 80

Why is the conservation of resources needed?

Answer 80

Non-renewable resources need to be conserved as stocks are finite. Alternative energy sources need to be implemented before non-renewable fuels run out. Plant products are renewable resources and include biofuels like alcohol, palm/sunflower oil, and wood.

Question 81

Why is recycling needed?

Answer 81

As minerals and resources become scarcer, they become more expensive, this will make reusing them more important. It can also be more energy efficient to reuse materials e.g. producing aluminium alloys from scrap metal uses about 5% of the energy it takes to make them from aluminium ores.

Question 82

How is sewage treated?

Answer 82

1. Screening: the sewage flows through a metal grid to remove larger solids, wood, plastic etc.
2. Grit: the sewage flows slowly through long channels and sand/grit settles at the bottom.
3. First settling tanks: liquid flows slowly, 40% of the organic material settles out as crude sludge
4. Aeration tanks: oxygen is added and aerobic bacteria digest leftover organic solids. Solids are converted into soluble nitrates, and then into nitrogen and carbon dioxide by different bacteria.
5. 2nd settling tanks: micro-organisms from the previous areas settle out, this sludge is returned to the aeration tanks.
6. When the sludge has settled the water is pure enough to return to waterways.

Question 83

What are the negative of female contraceptive hormones in water courses?

Answer 83

The hormone causes male frogs and fish to become ‘feminised’ whereby they start producing eggs in their testes instead of sperm. This causes an imbalance between the numbers of male and female animals.
Drinking water from treated sewage can also contain hormones. This has been shown to reduce the sperm count in men, causing a reduction in fertility.

Question 84

What is a sustainable resources?

Answer 84

A sustainable resource is one that is produced so rapidly as it is removed from the environment so that it does not run out.

Question 85

What are the effects of non-biodegradable plastics on the environment?

Answer 85

Plastics that are non-biodegradable are not broken down by decomposers when dumped in landfill sites or left as litter. Discarded plastic bottles can trap small animals; nylon fishing lines and nets can trap birds and mammals such as seals and dolphins. As the plastics in the water gradually deteriorate, they fragment into tiny pieces, which are eaten by fish and birds, making them ill. When plastic is burned, it can release toxic gases.

Question 86

What are the effects of sulfur dioxide and nitrogen oxides on the environment?

Answer 86

Sulfur dioxide, which is produced from the burning of coal and oil, and nitrogen oxides, which are produced from power stations and vehicle exhausts, dissolve in rainwater and form acid. This then comes down in acid rain which destroys forests, animals, and plants.

Question 87

What is the ‘greenhouse effect’?

Answer 87

When absorbs heat from the suns rays it radiates the sun’s energy back. The earth’s atmosphere acts as the glass in a greenhouse as it absorbs a lot of heat, but reduces the amount of heat that escapes. However gases and pollutants such as carbon dioxide, methane, nitrogen oxides, and CFCs absorb the most radiation. So an increase in these gases in the atmosphere would increase the greenhouse effect and result in global warming.