IGCSE Biology common questions and answers

Why do offspring look different to one another?

Because of random fertilisation and the effect the environment had had on their appearance

How many chromosomes are there in the human body?

There are 23 PAIRS

What is an allele?

A gene that codes for a different phenotype

Why do we divide by mitosis?

1.) To replace and repair damaged tissue

2.) In single celled organisms, to asexually reproduce

What is sexual reproduction?

The fusion of male and female gametes; the mixture of genetic information leads to variation

How do tumours grow?

Due to abnormal and uncontrolled cell growth

How do secondary tumours form?

Malignant tumours enter the blood stream and invade other healthy tissue

How can genes be CUT OUT for genetic manipulation?

1.) Enzymes are used to isolate the gene and it is the inserted into bacteria

2.) This vector (bacteria) is then able to insert the gene into the required cells

Tissue culture

1.) Produces genetically identical cells

2.) Small sections of the plant are remover, sterilised and then placed into a jelly growth medium

Embryo transplant

1.) The animal cells are SPLIT APRT before they can become specialised

2.) The identical embryos are then transplanted into host mothers

Adult cell cloning

1.) An unfertilised egg has its nucleus removed

2.) This is replaced by the nucleus from an adult body cell

3.) An electric shock is used to catalyse the reaction

4.) The cell then begins to divide

5.) The embryos is implanted into the host mother

How does DNA code for a protein?

1.) A sequence of 3 bases codes for a specific amino acid

2.) The sequence of bases codes for the sequence of amino acids

3.) Protein molecules are made up of chains of amino acids

Why does the stomach produce HCL?

To provide acidic conditions within which the enzymes in the stomach work best

How does bile aid the digestion system

1.) It neutralises the stomach acids which provides alkaline conditions within which the enzymes in the small intestine work best

2.) It emulsifies fat giving it a larger surface are which makes it easier for lipase to break it down

What is the purpose of the small intestine?

To break down starch, fat and protein into soluble substances so they can be absorbed into the blood stream

What happens to enzymes at very high temperatures?

1.) The high temperature causes the active sight to change shape

2.) Meaning they are unable to break down the substrate as it is unable to fit into the active sight

3.) So the enzyme is said to be denatured

Uses of enzymes in the industry

1.) Protease is used to pre digest protein in baby food

2.) Carboydrases are used to convert starch into sugar syrups

Uses of enzymes in the home

Biological detergents may contain lipase and protease because they are more effective at lower temperatures

What happens in a healthy liver?

1.) The excess amino acids are DEAMINATED to form ammonia that is converted into urea for excretion

2.) The poisonous substances are DETOXIFIED and the products are excreted in the urine

3.) The old blood cells are BROKEN DOWN but the iron is maintained

What happens in a healthy kidney?

1.) All of the blood is filtered

2.) All the glucose is reabsorbed

3.) As much water as needed is selectively reabsorbed through ADH

4.) The dissolved ions that are needed by the body are also absorbed

5.) Any excess ions and water are excreted alongside urea in urine

How do we INHALE?

1.) The INTERCOSTAL MUCLES contract which pulls the rib cage upwards

2.) The DIAPHRAGM MUSCLES contract to flatten the diaphragm

3.) This results in an increase in the volume of the thorax and the resultant decrease in external pressure causes air to rush into the lungs

How do we EXHALE?

Same as inhale but opposite

Which part of the brain is concerned with INTELLIGENCE, MEMORY and CONSCIOUSNESS?

The cerebral cortex

Which part of the brain is concerned with MUSCLE ACTIVITY?

The cerebellum

Which part of the brain is concerned with UNCONSCIOUS ACTIVITY?

The medulla

What is type 1 diabeties?

Where the pancreas does not produce enough insulin

What is type 2 diabeties?

Where the body does not respond to its own insulin

What is a pathogen?

A microorganism that causée an infectious disease

Why does bacteria make us feel ill?

Because they rapidly reproduce and release toxins

What do viruses do?

They rapidly reproduce within cells which causes damage

How do white blood cells defend us against pathogens?

1.) By ingesting the pathogen

2.) Producing specific antibodies to kill the pathogen

3.) Producing antitoxins that negate the effects of the toxins released by the bacteria

How does vaccination work?

1.) A dead or inactive form of the pathogen is injected into the patient

2.) This stimulates the red blood cells into producing specific antibodies to kill the specific pathogen

3.) Therefore of the pathogen arrives then the body is able to rapidly produce the correct antibody to kill the pathogen

What are painkillers?

Medicine that helps to relieve the symptoms of a particular disease

What are antibiotics?

Medicine that helps to cure disease by killing the bacteria

What effect has the over-use of antibiotics had on its effectiveness?

1.) It has made antibiotics less effective

2.) It kills the non resistant strain of the pathogen but a mutation occurs that allows certain strands to become resistant to the medicine

3.) Through natural selection, the resistant strain will be able to survive and pass on its successful characteristics

What is natural selection?

1.) Individual organisms within a particular species may show variation due to differences in their genes

2.) Those whose characteristics best suit the environment will be more likely to survive and reproduce

3.) Their successful characteristics will be passed on to their offspring

How do new species arise?

1.) Two populations of the same species become isolated from one another (geographically)

2.) Each population has a wide range of alleles that control their characteristics and leads to genetic variation

3.) The population who's characteristics best suit their environment will be most likely to survive and reproduce through natural selection

4.) The populations become so different that successful inbreeding is impossible

Why are scientists not sure about how life began on Earth?

Many early life forms were soft bodied so they have left very few traces due to geological activity

How does blood reach the lungs?

The right ventricle contracts and pumps blood along the pulmonary artery

How does blood reach all areas of the body?

The left ventricle contrats and sends blood along the aorta

What does blood plasma transport?

1.) CO2 from the organs to the lungs

2.) Soluble products of digestion

3.) Urea from the liver to the kidneys

How does blood clot?

1.) FIBRINOGEN changes into FIBRIN as part of an enzyme controlled reaction

The process of sexual reproduction in plants

1.) The anther produces the male gamete POLLEN GRAIN

2.) The pollen grain attaches to the STIGMA of a CARPEL within the female gamete OVULE

3.) The nuclei of the pollen grain migrate to the ovule and fertilise the egg

4.) The resulting zygote develops into an egg

5.) The ovule produces a seed

6.) The ovary grows into a FRUIT that grows around the seed

Translocation

The movement of dissolved sugars from the leaves to the rest of the plant along the PHLOEM TISSUE

Transpiration

The movement of water from the roots to the leaves through XYLEM TISSUE

How do plants use the glucose produces through photosynthesis?

1.) For respiration

2.) To make fats and oils

3.) To make proteins

Where does CO2 enter a plant?

Through he stomata

Why do plants respire?

To build up sugars, nitrates and other nutrients into amino acids which are then built into proteins

When is a plant cell considered TURGID

When placed in a HYPOTONIC SOLUTION

When is a plant cell considered PLASMOLISED

When placed in a HYPERTONIC SOLUTION

What are the three limiting factors of photosynthesis

1.) Temperature

2.) Light intensity

3.) CO2 concentration

What happens to the plant in high temperatures?

1.) The plants WILT

2.) This is because an increase in temperature cause an increase in the rate of transpiration

3.) The plant would be losing more water through the stomata than obtaining through the roots

Which part of the plant controls the size of the stomata

Guard cells

Experiment to show transpiration

Use a POTOMETER

What is phototropism

Where plants are sensitive to LIGHT

What is gravitropism

Where plants are sensitive to GRAVITY

What it hydrotropism

Where plants are sensitive to MOISTURE

What happens to a plant if the sun is shining from the LEFT hand side

1.) The plant will grow towards the light

2.) More auxin will grow on the shady side causing unequal distribution of auxin

3.) This causes cell elongation

Eutrophication

1.) The nitrate ions from fertilisers stimulates more algae growth on the surface of the river

2.) This means that light is unable to reach the bottom of the river

3.) The plants at the bottom are unable to photosynthesise so will die

4.) Microorganisms in the water decompose the dead vegetation through aerobic respiration

5.) This he's up the dissolved O2 in the water so organisms who require high amounts of dissolved O2 to survive will die off

Why does deforestation occur?

1.) To provide more space for cattle to grow

2.) To produce rice and oils for the developed world

3.) To produce crops that can be used in bio fuels

What effect does deforestation have on the environment?

It increase the concentration of CO2 in the atmosphere

1.) CO2 is released during combustion as trees are burnt

2.) Microorganisms decompose the dead trees through aerobic respiration which release CO2

3.) Less trees means less CO2 is 'locked up' in trees through photosynthesis

Where can CO2 be sequestered?

In Oceans, rivers and lakes

What is biomass?

The mass of living material

Why is biomass less at each stage in the food chain

1.) Energy is always lost during the organisms waste materials

2.) Much of the energy produces is eventually transferred into the surroundings

How is energy used in the body?

1.) Maintaining body temperature

2.) Movement

What are the concerns over embryo screening?

1.) May cause an unnecessary miscarriage

2.) questions over the termination of pregnancys

Structure of DNA

Long strands shaped as a double helix with 4 bases A, C, G, T

Uses of plant hormones

1.) Tissue culture

2.) Fertilisers

How does the body control the water concentration of the blood?

1.) The water concentration of the blood is controlled and detected by the pituitary glands

2.) If the concentration is to high then the glands releases less ADH

3.) This causes less water re-absorption the kidney which results in a less concentrated urine

4.) If the concentration is to low then more ADH is released by the glands

5.) This causes more water re-absorption in the kidney and results in a more concentrated urine

What does an animal cell have?

1.) A cell membrane

2.) Cytoplasm

3.) Mitochondria

4.) Ribosomes

5.) Nucleus

What does a plant cell have that an animal cell does not?

1.) A cell wall,

2.) A permanent vacuole,

3.) Chloroplasts

What does a bacteria cell have that an animal cell does not?

1.) A flagellum

2.) Plasmid DNA

How does shivering help heat the body?

This contraction requires respiration and the energy released can warm the body

What is pollination?

The transfer of male gametes to the female ovules

How can embryos be screened for genetic faults?

1.) The DNA is isolated from the embryo cells

2.) A gene probe will bind onto the gene for a specific disorder

3.) This normally has a colourful chemical attached to it

4.) The probe is added to a mixture containing the DNA sample

5.) UV light is used to detect the disorder

What are the benefits of GM crops?

1.) They are résistant to attack from insects

2.) They show much higher yields

Concerns about GM

What are the effects of it on wild flowers and humans when eaten

Adaptations of the TAPE WORM

1.) They have suckers and hooks to fix themselves to the wall of the intestine

2.) They have flattened sections of their body to produce a large number of eggs

3.) They have no gut, their flattened shape provides a large surface area for the absorption of soluble products from the host

4.) Has a thick outer cubicle to protect itself from the host's digestive enzymes

How do fossiles form?

1.) From parts of organisms that have not decayed because one or more of the conditions required for decay was absent

2.) When parts of the organism is replaced by other materials they decay

3.) As preserved traces i.e. Footprints

Why does a single celled organism not require complex structures for diffusion?

Because they have a high surface area to volume ratio so all the exchanges occur via its surface membrane

What are complex carbohydrates?

Long chains of simple sugar units bonded together ie. Starch

What happens to the human body during exercise?

1.) The heart rate increases which increases blood flow to the muscles,

2.) Rate and depth or breathing increases,

3.) Glycogen is turned back into glucose

What happens to haemoglobin in the lungs?

It reacts with oxygen to form OXYhaemoglonin

What happens during photosynthesis?

1.) Light energy is absorbed by the chlorophyll,

2.) This energy is used to convert CO2 (from AIR) and WATER (from SOIL) into glucose

What is pollination?

The transfer of male gametes to the female ovules

What is tissue?

A group of cells with similar function

What is therapeutic cloning?

Where and embryo containing the same genes as the patient is produced

What occurs in the large intestine?

Where the water from indigestes food is absorbed which produces faeces

What are carbohydrases

Molecules made up of sugar

How can isomerase be used in the industry?

It converts glucose syrup into fructose syrup which is much sweeter so can be used in smaller quantities

What're antigens!

Proteins on the surface of cells

How can we map the brain?

Using electrical simulation and MRI scans

How do plants prevent wilting?

The guard cells close the stomata x

How can we prevent the decline in fish stocks?

Use fishing quotas and assign net sizes

How can we remove random errors?

By repeating and calculating a new mean

What is a systematic error?

An error that is always the same for every repeat, usually because of how the experiment is set up

What is a zero error?

Where the instrument e.g. Measuring cylinder does not start at 0

Where is bile produced?

In the liver

How do you develop cultures of Microorganisms for investigation?

- Sterilise pétri dishes before use to remove unwanted Microorganisms

- The incubating loops must be sterilised

- Lid must be secured with tape to prevent Microorganisms from the air from contaminating the results

What is a dominant allele?

An allele that controls the characteristic when present on only one of the chromosomes