Biology GCSE

What are the parts of an animal (and plant) cell?

Nucleus
Cytoplasm
Cell membrane
Mitochondria

What are parts of a plant cell?

Rigid cell wall
Large vacuole
Chloroplasts
(nucleus, cytoplasm, cell membrane and mitochondria)

What does the nucleus do?

Contains DNA that controls what the cell does

What does the cytoplasm do?

Its a gel-like substance where most of the chemical reactions happpen

What does the cell membrane do?

Holds the cell together and controls what goes in and out

What does the mitochondria do?

This is where most of the reactions for respiration take place. Respiration releases energy that the cell needs to work.

What does the rigid cell wall do?

It is made up of cellulose and it gives support for the cell

What does the large vacuole do?

Contains cell sap, a weak solution of sugar and salts

What do chloroplasts do?

This is where photosynthesis occurs. They contain a green substance called chlorophyll.

What are the features of a bacteria cell?

Chromosomal DNA
Plasmids
Flagellum
Cell wall

What is chromosomal DNA?

Chromosomal DNA controls the cells activities and replication. It floats free in the cytoplasm.

What are plasmids?

Plasmids are small loops of extra DNA that aren't part of the chromosome. Plasmids contain genes for things like drug resistance and can be passed between bacteria.

What is the flagellum?

The flagellum is a long, hair-like structure that rotates to make the bacterium move.

What does the cell wall do?

Support the cell

What is magnification?

How much bigger the image is that the specimen

How do you work out magnification?

length of image / length of specimen

What is the difference between light microscopes and electron microscopes?

Light microscopes let us see things like the nuclei, chloroplasts and mitochondria. Electron microscopes let us see much smaller things in more detail like the internal structure of mitochondria and chloroplasts and even tinier things like plasmids.

What is DNA?

DNA is the complex chemical that carries genetic information. DNA is found in chromosomes which are found in the nucleus of most cells.

What is the structure of DNA? (6marker)

-A DNA molecule has two strands coiled together in the shape of a double helix.
-The two strands are hold together by chemicals called bases. The four bases are adenine, thymine, guanine and cytosine.
-The bases are paired, and they always pair up in the same way; A-T and C-G. This is called base pairing.
-The base pairs are joined together by weak hydrogen bonds.

What is a gene?

A gene is a short piece of DNA that codes for a specific protein. You have genes for hair structure, eye colour enzymes and every other protein in your body.

Who discovered the structure of DNA?

-Rosalind Franklin and Maurice Wilkins worked out DNA had a helical structure by directing beams of X-rays onto crystallised DNA and looking at the patterns of x-rays formed as they bounced off.
-James Watson and Francis Crick used these ideas along with the idea the amount of adenine+guanine matched the amount of thymine+cytosine to make a model of the DNA molecule where all the pieces fitted together.

What would be a practical to extract DNA?(6 marker)

-Mash or chop fruit or vegetable (e.g kiwi) and mix with salty water and detergent to break open the cells and help release the DNA from the nuclei.
-Add protease enzyme to the filtered mixture to break up proteins in cell membranes and so release more DNA.
-Add ice cold ethanol carefully down inside the tube into the mixture. The ethanol makes the DNA separate from the liquid so it is easy to lift out.

How does a cell make proteins?

By stringing amino acids together in a particular order. There's only 20 different amino acids that are used to make up thousands of different proteins. The order of bases in a gene tells cells in what order to put the amino acids together. Each set of three bases (triplet) codes for a particular amino acid.

What can DNA determine?

Which genes are switched on or off and so which proteins the cell produces e.g keratin. That in turn determines what type of cell it is e.g. red blood cell, skin cell.

What are proteins made by?

Proteins are made in the cell by oraganelles called ribosomes.

Why does the cell need mRNA?

Because DNA is found in the nucleus and can't move out of it because its too big. The cell needs to get the information from the DNA to the ribosome in the cell cytoplasm. This is done by using a molecule called mRNA, which is very similar to DNA, but it's shorter and only a single strand. Also, instead of thymine, mRNA has the base uracil (u), which pairs with adenine. mRNA is like a messanger between the DNA in the nucleus and the ribosome. It happens during transcription and translation.

What happens during transcription?

-Transcription takes place in the nucleus.
-The weak hydrogen bonds break and a section of DNA is unwound and the two strands separate.
-One strand is used as a template.
-Complementary bases to this strand link to it.
-mRNA is formed.
-mRNA stands for messenger RNA
-mRNA moves out of the nucleus into the cells cytoplasm

What happens during translation?

-Translation takes place in the cytoplasm when the mRNA attaches to a ribosome.
-The ribosome moves along the mRNA in one direction reading a triplet of bases (codon) at a time.
-tRNA molecules bring amino acids to thee ribosome. The amino acids attached to each tRNA molecule depends on the order of bases in the tRNA.
-Complementary bases of tRNA pair with the bases of the mRNA strand.
-Amino acids that are close together are joined to make an amino acid chain (a polypeptide)
-Every protein is formed from a specific number of amino acids in a particular order. The order of the bases in the DNA defines the order in which the amino acids are joined together. So one section of DNA codes for one particular protein.

What do mutations do?

A mutation is a change in an organisms DNA base sequence. This may change the amino acid that is added to the chain during translation on the ribosome.

What could a harmful mutation change do?

A harmful mutation could cause a genetic disorder, for example, cystic fibrosis

What can a beneficial mutation do?

A beneficial mutation could produce a new characteristic that is beneficial to an organism e.g. a mutation in genes on bacterial plasmids can make them resistant to antibiotics

What can neutral mutations do?

Some mutations are neither harmful nor beneficial e.g. they don't affect a proteins function

What does the haemoglobin (in blood) do?

Carries oxygen to red blood cells. They have a globular shape

What do hormones do?

Hormones are transported in blood to target cells. They have a globular shape

What does the collagen do?

The collagen is in tendons and ligaments. Ligaments hold bones together and tendons attach muscles to bones.

Why does the shape of a protein matter?

The shape of a protein affects the way it works. The sequence of amino acids gives each protein a particular 3D shape. These shapes may be globular (blobbly) or fibrous (long,strong fibres)

Enzymes have a very specific shape that allows them to work effectively. Why might a gene with a mutation change the activity of an enzyme? Refer to active site in your answer

A gene mutation can change the base sequence in DNA. If this change produces a different amino acid sequence, this may change the shape of the active site. The shape of the active site controls how well an enzyme works. If the shape of the active site matches the shape of the substrate better, then the enzyme will work better. But if the shape of the active site is not as good a match, then the enzyme will not work so well.

What are enzymes?

Enzymes are biological catalysts that control reactions in the body.

What is a catalyst?

A catalyst is a substrate which increases the speed of a reaction without being changed or used up in the reaction.

What is meant by the 'lock and key' hypothesis for enzymes?

Each enzyme has an active site. Some substrates may or may not fit the active site. If the substrate matches the shape of the active site, the substrate molecules hold them close together so bonds can form between them and make a product. If the product molecule doesn't fit the active site, it is released from the enzyme. Enzymes usually only join with one substrate as they have a high specificity for their substrates.

How would someone measure the rate of a reaction by using amylase as the enzyme and starch substrate?

-Amylase catalyses the breakdown of starch. So you time how long it takes for the starch to dissappear
-To do this, regularly take a drop of the amylase and starch mixture, and put it into a drop of iodine solution on a spotting tile. Record the colour change - it will true blue-black if starch is present. Note the time when the iodine solution no longer turns blue-black - the starch has then been broken down by the amylase. You can use times to compare reaction rates under different conditions.

What are the variables you may change during an enzyme controlled reaction?

-Changing the temperature = put test tubes into different temperature water baths
-Effect of pH = use a range of different pH buffers
-Effect of substrate concentration = vary the substance concentrations of the starch solutions

What happens at lower temperatures to molecules and how does this link to the 'lock and key' hypothesis?

At lower temperatures, molecules move more slowly. So substrate molecules take longer to fit into and react in the active site.

What is the optimum temperature?

The temperature where the enzyme is working at the fastest rate

What can higher temperatures cause the active site to do?

Higher temperatures cause the active site to change shape, so it cant hold the substrate as tightly and the reaction goes more slowly.

What happens to the active site at very high temperatures?

At very high temperatures the active site breaks up and the enzyme is denatured.

How does the pH effect an enzyme?

If the pH is too high or too low, it interferes with the bonds holding the enzyme together. This changes the shape of the active site and denatures the enzyme.

What is an optimum pH for an enzyme?

The optimum pH for an enzyme is the pH that they work best at. This is often neutral pH 7, but not always.

How does substrate concentration effect an enzyme?

The higher the substrate concentration, the faster the enzyme will react with substrate molecules. However, after adding so many substrate molecules eventually if you add more it will make no difference.

What is the human genome project?

Scientists in 18 different countries collaborated to decode the human genome. This is the order of bases on all the human chromosomes. The project was completed quickly because so many scientists worked on it at the same time. The work was published in 2003.

What are the positives of the human genome project?

-It helps predict and prevent diseases. (This helps early detection and helps cures to be discovered)
-Develop new and better medicines.
-Accurate diagnoses
-Improved forensic science (DNA fingerprint found on crime scenes)

What are the negatives of the human genome project?

-Increased stress (People could easily panic if they are away the may have a disease)
-Gene-ism (People with genetic problems could come under pressure not to have children)
-Discrimination by employees and insurers (life insurance could be very expensive if you are likely to get a disease)

What are two possible developments as a result of decoding the human genome?

-Identification of genes that can cause disease
-Gene therapy (involves replacing faulty alleles in body cells with healthy ones. This would allow the effected person to live a normal healthy life)

What is genetic engineering?

Scientists can remove a gene from one organism and insert it into the DNA of another organism.

What are the steps of genetic engineering?

1. A gene is cut out of chromosome using restriction enzymes.

2. A DNA plasmid is taken out of a bacterium and cut open using enzymes

3. The gene and the plasmid are mixed together.

4. The Gene and the plasmid are stuck together using lypase enzymes to make a new plasmid

5. The new plasmid with the gene is put into a bacterium. The bacterium has been genetically modified and will now make the ....

How can genetic engineering help reduce vitamin A deficiency?

1)Beta-carotene is used by our bodies to make vitamin A. Vitamin A deficiency is a big problem in parts of south Asia and Africa. It can cause people to go blind.
2) Golden Rice is a variety of GM rice. It contains two genes from other organisms which together enable the rice to produce beta-carotene. So fewer people will suffer from vitamin A deficiency if they eat golden rice.

How can genetic engineering help produce human insulin?

The human insulin gene can be inserted into bacteria to produce human insulin. Lots of human insulin can be produced quickly and cheaply to treat diabetes.

How can genetic engineering increase crop yield?

GM crops have had their genes modified e.g to make them resistant to herbicides. Fields of these crops can be sprayed with a herbicide and all the plants except GM crop are killed. This can increase the yield of the crop making more food.

Why do some people thing genetic engineering is a bad thing?

Some people are worried about the long-term effects of genetic engineering, that it may create some unplanned problems such as:
-Some thing GM crops will affect the number of weeds and flowers (therefore wildlife) that usually lives in and around the crops - reducing farmland biodiversity
-Not everyone is convinced that GM crops are safe, people worry the may develop allergies to the food
-Some worry transplanted genes may get out into the natural environment e.g herbicide resistance may be picked up by weeds creating a superweed.

What are diploid cells?

Cells that have two sets of chromosomes. Human body cells are diploid.

What is mitosis?

How cells divide for growth and repair. This happens when humans, animals and plants want to grow or replace cells that have been damaged.

What are the stages of mitosis?

-The parent cell is a diploid cell (it has two sets of chromosomes). Before the parent cell divides, each chromosome is copied exactly. The parent cell divides to form two daughter cells that are genetically identical to each other and the parent cells (these are also diploid cells)

What are situations where mitosis is used to produce new cells?

-Growth
-Repairing damaged parts of the body
-Asexual reproduction

What is asexual reproduction?

Asexual reproduction is the production of new organisms without fertilisation. The offspring have exactly the same genes as the parent - so there's no genetic variation.

When might asexual reproduction happen?

-When bacteria split to make more bacteria
-When plants make new plantlets that split off from the parent plant to grow on their own.

What are gametes?

Gametes are 'sex cells'. They are called ova (single ovum) and sperm in males. During sexual reproduction, two gametes combine to form a new cell which will grow to become a new organism.

What are haploid cells?

Haploid cells have only one copy of each chromosome. Gametes are haploid.

Why are gametes haploid?

So that when two gametes combine at fertillisation, the resulting cell (zygote) has the right number of chromosomes. Zygotes are diploid - they have two copies of each chromosome.

What is meiosis?

Meiosis is when a cell divides to produce four haploid nuclei whose chromosomes are NOT identical. Meiosis only happens in reproductive organs e.g ovaries

What happens during meiosis?

As with meiosis, before the parent cell begins to divide, each chromosome is copied. The cell divides in two and then in two again. Four daughter cells are produces. Each daughter cell gets a copy of one chromosome from each pair. Each daughter cell has only one set of chromosomes therefore these are haploid cells. The daughter cells are not all identical - meiosis results in variation.

What happens during sexual reproduction?

During sexual reproduction, two gametes for a new cell which will grow to become a new organism. The two gametes combine (sperm and egg) to produce a zygote (fertilised egg). Sexual reproduction produces variation in the offspring.

What is cloning?

Cloning is a type of asexual reproduction. It produces cells that are genetically identical to an original cell.

What are clones?

Clones are organisms that have identical genes.

How is cloning done?

1. The nucleus is removed from an egg cell

2. The diploid nucleus is removed from an adult body cell.

3. The diploid nucleus from the body cell is placed inside the empty egg cell. The cell is then stimulated with an electric pulse to start mitotic division.

4. The cell divides and grows as an embryo

5. The embryo is placed in the uterus of a surrogate mother until it is ready to be born.

What are the advantages of cloning?

• If the animal that is cloned has good features, all of its offspring will have the same good features.

• Cloning mammals can help with the shortage of organs for transplants

• Cloning can be used to help preserve endangered species

What are the disadvantages of cloning and some issues surrounding cloning?

• Any genetic defect in the parent will be passed on to the offspring

• Clones mammals may suffer more health problems than usual, which may cause them to die early

• It is more difficult to clone a mammal than a plant; it may take a few attempts

• Cloning mammals leads to a reduced gene pool (fewer alleles in the population). This may mean if there is a new disease all the species could become extinct

What are stem cells?

Stem cells are cells that can divide to produce many types of cell. There are two kinds of stem cell; embryonic and adult stem cells.

What are embryonic stem cells?

Embryonic stem cells are taken from embryos that contain only a few cells. The cells in the embryo are all the same (undifferentiated). Stem cells are easy to extract from an embryo. They can also produce any type of cell.

What are adult stem cells?

Adult stem cells are found in differentiated tissue, such as bone or skin - they divide to replace damaged cells. No embryo is destroyed so there's no ethical issue. If adult stem cells are taken from the person to be treated, it will not cause rejection to the body.

What are disadvantages to using embryonic stem cells?

-The embryo is destroyed when the cells are removed and some people think embryos have a right to life
- The body recognises the cells are different and will reject them without the use of drugs.

What are the disadvantages of adult stem cells?

-They are difficult to find and extract from tissue
-They produce only a few types of cell

What is a risk of using stem cells?

They may produce cancer cells instead of healthy cells

What is respiration?

Respiration is the process used by all living organisms to release energy from organic molecules. Respiration is how all living things get energy from food.

What is the energy from respiration used for?

• Growth and movement

• Build up larger molecules (like proteins)

• Contract muscles

• Maintain a steady body temperature

What is aerobic respiration?

Aerobic respiration uses oxygen from the air to release energy from glucose.

What is the word equation for aerobic respiration?

Glucose + Oxygen = Carbon dioxide + water (+energy)

What is anaerobic respiration?

Anaerobic respiration is the release of energy from glucose without using oxygen. This produces lactic acid.

What is the word equation for anaerobic respiration?

Glucose = lactic acid (+energy)

When is anaerobic respiration used?

Anaerobic respiration happens when there's not enough oxygen available. Anaerobic respiration does not release as much energy as aerobic respiration. It also produces build up of lactic acid in the muscles which gets painful and can give you cramp.

What is the advantage to using anaerobic respiration?

You can keep on using your muscles for longer. Anaerobic respiration is useful for muscle cells because it can release energy to allow muscles to contract when the heart and lungs cannot deliver oxygen and glucose fast enough for aerobic respiration.

What is the disadvantage to using anaerobic respiration?

-Anaerobic respiration releases much less energy from each molecule of glucose than aerobic respiration.
-Lactic acid is not removed from the body. It builds up in muscle and blood, and must be broken down after exercise.

What is EPOC?

EPOC (excess post-exercise oxygen consumption) is the amount of oxygen needed after exercise has ended compared with the resting rate.

What is diffusion?

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.

When is diffusion used?

Many substances enter and leave the body by diffusion. These substances include gases such as oxygen and carbon dioxide, and small digested food molecules such as glucose.

Why is diffusion needed?

-When cells respire they use up oxygen and glucose, so the concentration of these inside the cells is low. The concentration of these substances in the blood is higher, so they diffuse from the capillaries into the cells.
-When cells respire they produce carbon dioxide therefore the concentration is high. The carbon dioxide diffuses from the cells into the blood where the concentration is lower.

Why do you respire more during exercise?

Muscles need energy from respiration to contract. When you exercise some of your muscles contract more frequently than normal so you need more energy. This energy comes from increased respiration. The increase in respiration means you get more oxygen to the cells.

Why is it important that you breathing rate increases during exercise?

Your breathing rate increases to get more oxygen into the blood around the body so your heart rate increases. This removes CO2 more quickly at the same time.

How do you calculate cardiac output?

Cardiac output = heart rate * stroke volume

How could you investigate the effect of exercise on breathing and heart rate?

-You can measure breathing rate by counting breaths and heart rate by taking a pulse.
-You could exercise for 5 minutes doing three different exercises of different intensities. After each exercise take your pulse and heart rate.
-Your pulse rate will increase the more intense the exercise is as your body needs to get more oxygen to the muscles ad take away the carbon dioxide.

What is photosynthesis?

Photosynthesis is the process that plants use to make glucose.