GCSE EDEXEL BIOLOGY

Why is Mitosis important?

Mitosis is important because all living things need to be able to grow and repair itself.

What does asexual reproduction mean in terms of chromosomes?

Asexual reproduction is the creating of offspring with only ONE parent. This means there is no variation between parent and offspring. This means that in mitosis, the parent cell makes two cells identical to the original cell so they have exactly the same number of chromosomes in their nuclei.

What are the stages of Mitosis?

Interphase interphase prophase metaphase anaphase telophase cytokinesis interphase

Explain the stages of Mitosis

Interphase- normal cell with 46 chromosomes

Interphase- the cell produces extra sub-cellular parts for the new cell and doubles its chromosomes

Prophase- the chromosomes condense, become shorter thicker more visible chromatids

Metaphase- the chromatids line up at the centromere. Spindle fibres start to form

Anaphase- the spindle fibres contract, pulling apart the chromosomes

Telophase- the membrane forms around each set of chromosomes

Cytokinesis- the nuclear envelope reforms around each new cell

Interphase- finished!

What is cell differentiation?

The process by which a cell changes to become specialised for it's job.

What are meristems?

A group of cells at the very end of a shoot of a plant which are able to divide by mitosis very rapidly. They keep the plant growing for a long time. These cells are then able to get longer by elongation and specialise by differentiation.

How do you calculate growth in plants?

final value- starting value

------------------------------ x 100

starting value

What are stem cells, where can they found?

Stem cells are undifferentiated cells that have the potential to develop into any specialised cell. In humans, they are found in very early embryos (developed right after meiosis. They are also found in adult bone marrow however these are less versatile. In plants they are found in the meristems.

What are some draw backs of using stem cells in medicine?

-Virus spreading

-Rejection in the patients body

-tumour/ cancer development (uncontrolled dividing of the stem cells)

-ethical reasons

What different parts pf the brain are there

-cerebrum

has two halves called the cerebral hemispheres

Right side controls muscles on the left side of the body

-cerebellum

controls muscle coordination and balance

-Medulla oblongata

controls subconscious movements like blinking and breathing

How does a CT scan work?

X-ray beams move in circles around the brain. The absorption of the x-rays is measured and a computer can build up pictures of 'slices' of the shapes and structures in the brain.

How does a PET scan work?

The patient is injected with a radioactive isotope like glucose. More active cells in the brain need more glucose for respiration so take on more. The radioactive atoms release gamma rays which can be picked up by a scanner, coming from the more active parts of the brain.

What is quadriplegia and why is it hard to repair?

Quadriplegia is when damage of the neck causes loss of the use of the legs and arms. There are no adult stem cells that can differentiate into neurones. However, wires can be sued to electrically stimulate neurones below the damage, but the patient wont regain full usage.

How can tumorous cancers be treated and why might the methods not work?

They can be treated with radiotherapy, which are high energy x ray beams, or chemotherapy which are rugs that kill actively dividing cells. It may not work due to the blood-brain barrier, which is a natural filter which only allows certain substances from the blood to the brain.

Explain how the CNS coordinates a response to a stimulus

Firstly, the stimulus (a change in environment) is detected by the receptor cells. These could be in the eye if the stimulus is light or in the hand if it's pressure or touch. The stimulus is converted to an electrical impulse which is sent to CNS. The CNS coordinates a response, and this information is relayed through the CNS and to a motor neurones with relay neurones. The electrical impulse is sent through the motor neurone to the effector. The effector then carries out of the according response.

What does a sensory neurone look like?

A sensory neurone is made up of one long Dendron, with receptor cells at one end, and at the other end (in the direction of the electrical impulse) there is the cell body. The cell body attaches onto the axon which carries the impulse onto frequent axon terminals so the impulse can be transferred to other neurones. There is myelin sheath around which acts as an electrical insulator, speeding up the impulse and stopping it from getting lost.

Why are axons and Dendrons often long?

To allow fast neurotransmission over long distances.

Explain the structure of a motor neurone

A motor neurone has many short dendrites carrying impulses from the CNS to the cell body. One long axon carries nerve impulses from the cell body to the effector cells.

Explain the structure of a relay neurone

Has many short dendrites which carry information from the sensory neurones to the cell body. An axon carries the impulse to motor neurones from the cell body. More circular looking.

What is a synapse?

Synapses connect two neurones, so is basically the gap between the end and start of two neurones. The nerve signal is transmitted by chemicals called neurotransmitters that then set off the electrical impulse in the next neurone. The transmission of nerve impulses is really fast but is slowed down a little bit ad the chemicals diffuse over the synaptic space.

What is a reflex?

A reflex is an automatic, rapid response to stimuli. They are used to reduce the chances of being injured. The route a reflex takes is called a reflex arc and they go through the spinal cord or an unconscious part of the brain. A stimulus is detected by receptor cells and sent a long a sensory neurone to the spinal cord or part of the brain. In the CNS, the impulse is passed through a relay neurone to a motor neurone, along the motor neurone and eventually to the effector. The muscle then contracts or responds accordingly. CROSS FEWER SYNAPSE= FASTER

What is a good example of a reflex?

The Iris reflex

Very bright light can damage the retina, so reflex takes place to contract the circular muscles in the iris to make the pupil smaller and therefore take in less light.

What is the retina in the eye?

The retina is a layer that contains receptor cells. Cones are receptor cells which are sensitive to different colours of light. Cones generate impulses that travel through a sensory neurones to the optic nerve. The impulses are processed into full colour visible light at the back of the cerebral hemispheres. Rods are receptor cells which are sensitive to light intensity, so work in dim light, which is why your colour vision is worse in dim light.

What is the pupil in the eye?

The pupil is the dark part in the middle of the eye, where light enters. The amount of light that enters is controlled by the iris, the coloured part of the eye, which can constrict or dilate the pupil to let in more or less light.

What is the cornea?

The cornea is a clear layer over the eye that focuses light onto a point on the retina to produce a clear image. The cornea refracts light rays to bring them together. The lens, the large part of eye, fine tunes the focusing and the ciliary muscles make the lens fatter to focus objects that are near and thinner to focus objects in the distance.

How does the eye focus on close and far away objects?

For distant objects, the ciliary muscles relax, making suspensory ligaments pull tight, producing a less rounded shape of the lens. to look at close objects, the ciliary muscles contract, forcing the suspensory ligaments to slacken so the lens becomes a more rounded shape.

What is sexual reproduction? What does it produce?

Sexual reproduction is when genetic information from two organisms combine to produce genetically different offspring. In sexual reproduction, the father and mother produce gametes. So in males it produces sperm and is females it produces egg cells.

What is a gamete?

A gamete is a cell that only contains half the number of chromosomes than a usual cell, so it is haploid as opposed to diploid.

What happens at fertilisation?

At fertilisation, the male gamete fuses with the female gamete to produce a fertilised egg or a zygote. The zygote undergoes mitosis to develop into an embryo. The embryo has a mixture of characteristics from it's mum and it's dad.

What happens in meiosis ( sexual reproduction)?

It happens in the reproductive organs. There are two divisions. In the first division, firstly the cell duplicates it's DNA. The chromosomes line up in pairs in the centre of the cell. One chromosome each pair came from it's mother and one from it's father. The pairs are then pulled apart, with some of the fathers and some of the mother's chromosomes going in each new cell. Each new cell contains a mixture of the father and mother's DNA. The mixture of this DNA at the prophase stage is important because it causes genetic variation. In the second division, the chromosomes again line up at the centre of the cell. The arms of the chromosomes are pulled apart. You now have four diploid daughter cells and each are genetically different.

What is a chromosome?

A chromosome contains one long molecule of DNA tightly coiled up many times. Proteins hold the shape.

What is DNA's structure made up of?

DNA forms the shape of a double helix. The strands of the double helix are formed by sugars and phosphates. The rungs of the double helix are made up by bases, A T C and G, which are complimentarily paired together with hydrogen bonds. Each base is attached to a sugar and each sugar is attached to a phosphate and this is nucleotides. For this reason, DNA is a polymer as it is a chain of similar units.

What is a genome?

All of organism's DNA.

Why do human's need proteins?

Cell structure

For our hair and nails

For enzymes and chemical reactions

For hormones

For our skin

What is the aim of transcription?

The aim of transcription is to get DNA out of the nucleus into the cytoplasm of the ribosomes where it can be used to make proteins. The DNA can't easily come out of the nucleus because it is too large.

Explain what happens in transcription?

In transcription, an enzyme called RNA polymerase attaches to the DNA in the nucleus and 'unzips' it, breaking apart the hydrogen bonds. This forms a template strand and a coding strand. RNA base joins to the template strand, replacing Thymine with Uracil. This new strand is called messenger RNA (mRNA) and is small enough to sneak out nucleus into the cytoplasm by the nuclear pores.

What is translation?

In translation, the mRNA joins to a ribosome, which 'reads' the mRNA in it's codons (its base triplets). Another molecule called tRNA brings the amino acid which is complimentary to that codon. The amino acids line up and join together to from a polypeptide chain which can then fold up and form a particular shaped protein.

What is a phenotype?

A phenotype is the observable characteristics of an organism.

What is a mutation?

A mutation is a change in the bases of a gene. Mutation are the reasons genes exist in different forms called alleles.

What is sickle cell disease?

Sickle cell disease is caused by a mutation in haemoglobin, where red blood cells become sickle shaped and stick together ,resulting in episodes of immense pain.

What can a mutation in the non coding part of DNA cause?

RNA polymerase attaches to a region of non-coding DNA in front of the gene. If there is a mutation here, it can affect how well RNA polymerase can attach. It can make it easier or harder. This will affect how much mRNA is transcribed and therefore how much protein is made. The phenotype of the organism may be affected by the amount of protein made.

Who was Mendel and what did he discover?

Mendel was an Austrian Monk who observed peas in his monastery garden. He noticed that characteristics of peas off spring where either absent or present and where not a blend of their parents characteristics. He concluded that different 'factors' or alleles control the variation of characteristics

What's the difference between a gene ( a characteristic) and an allele?

The gene may be hair colour, but the allele will be which specific hair colour like red or brown or black.

Why did scientists mainly ignore Mendel's work?

They said that if factors couldn't change, they couldn't evolve so how could evolution be possible (Darwin's theory)

What does homozygous mean?

Homozygous means both alleles that code for a gene in an organisms genome are the SAME. This means for sure the organism's phenotype will turn out this way.

What does heterozygous mean?

Heterozygous means the two alleles that code for the same gene in an organism's genotype are different. This means the organism's phenotype will turn out according to the DOMINANT allele.

When does a recessive allele show in an organisms phenotype?

When both alleles present for that gene are recessive.

How can a genetic diagram show the inheritance of different characteristics?

A lower case letter represents a recessive allele, and a capital letter represents a dominant allele. This way the ratio of offspring who will show a characteristic.

What is a carrier?

A carrier carries a recessive allele for a disease like cystic fibrosis but doesn't show the characteristics, but may pass it on to their offspring. If two carriers have offspring, the off spring might then have cystic fibrosis.

How is the inheritance of blood groups different from the inheritance of other alleles?

There are multiple alleles for the inheritance of blood group. There are four potential blood types, O, A, B and AB. There are three different alleles called IA, IB and IO. IA and IB are co dominant. This means that when an individual has both these alleles, they'll have the blood type AB. Neither allele is more dominant. However IO is recessive so you only get blood type O if you get two recessive IO alleles.

What is the Human Genome Project?

Thousands of scientists from all over the world collaboratively worked together to map every single human gene. The project started in 1990 and a complete map of the human genome, including the location of over 20000 genes was completed in 2003. Thanks to the Human Genome Project, scientists can now identify the genes and alleles that are suspected to cause an inherited disease much faster. They can develop better medicines and treatments.

How are fossils evidence for human evolution?

Evidence from fossils suggest humans and chimpanzees evolved from a common ancestor that existed around 6 million years ago.

Which fossils contributed towards evidence for human evolution?

-Ardi (Ardipethicus ramidus) was found in Ethiopia from around 4.4. million years ago. She ahd big ape like toes. She had long arms and short legs like an ape and a smaller brain. Lucy is about 3.2 million years ago. She was more human like than Ardi. She had arched feet more adapted to walking than climbing. Her brain was larger. The species homo-erectus was from 1.6 million years ago and he was even more human like.

What other evidence for evolution was there?

-development of stone tools

-the pentadactyl limb is a limb with 5 digits. It can be found in many species, suggesting all species with a pentadactyl limb evolved from the same common ancestor, e.g. bats and humans.

What are the three groups of classification of animals?

1) Archaea

2)Bacteria, true bacteria

3)Eukarya which include a broad range of organisms including fungi plants, animals

What is Tissue Culture and how is it done?

This is reproducing tissue from a single individual instead of going through the lengthy process of selective breeding to get there. Plants made this way are clones. Frist you select the plant you want to clone. Then you take tissue from it's fast growing root or shoot tips. You grow the tissue in a growth medium using nutrients and growth hormones. This is done under aseptic conditions to prevent the growth of potentially harmful microbes. The tissue can then be transferred to potting compost to carry on growing.

How is tissue culture of animal cells carried out?

Firstly, the tissue you want is extracted from the animal. The cells are separated from each other using restriction enzymes The DNA is cut out so it has 'sticky ends' meaning the ends of the DNA can rebond. Then thy are placed in a culture vessel, inserted into the plasmid, bathed in a growth medium which allows them to grow and multiply. The modified plasmid can then be placed into the bacterium or a different vessel.

How can genetic engineering be useful in medicine and agriculture?

Crops can be modified to be resistant to herbicides (chemicals that kill plants). This means a farmer can spray a crop to eradicate the weeds that sue up the nutrients without actually killing his crop so they can grow to maximum yield. In medicine, scientists have genetically engineered bacteria to produce insulin.

What is a vector?

A vector is an organism that does not cause disease to itself, but carries infection by transferring pathogens to other hosts. For example, a mosquito is a vector for the disease malaria.

How health defined by the World Health Organisation?

A complete of state of physical, mental and social well being, and not merely the absence of disease or infirmity.

What are pathogens ?

Pathogens are organisms such as viruses, bacteria, fungi and protists

How does cholera spread and what is it?

Cholera is spread by a bacterium pathogen. Its symptoms are vomiting and diarrhoea. It's spread in contaminated in water sources. Making sure people have access to clean water will prevent it.

What is a virus and how does it reproduce?

A virus is no more than a strand of genetic material encases in a protein coat. This means to reproduce the virus needs to infect a host cell. Many will the reproduce with the lytic pathway but some go through the lysogenic pathway first.

What is the lytic pathway?

The virus attaches itself to a host cell.