AQA-GCSE Biology Topic 6

• What are chromosomes?

  They are really long molecules of DNA
• What does DNA stand for

  DeoxyribonNucleicAcid. It is a complex chemical in a thread-like chain. It contains coded information and genetic information
• Where is DNA found

  It is found in the nucleus of animal and plant cells in long structures called chromosomes. Chromosomes normally come in pairs
• What is DNA structure called

  It is a polymer. It is made up of two strands coiled together in the shape of a double helix.
• What is a gene


  It is a small section of DNA found on a chromosome. Each gene codes a particular sequence of amino which are put together to make a specific protein. Tells the order to put the amino acids together.
• How many acids are used to make a specific protein

  20 amino acids are used to make up thousands of different proteins.
• What does DNA determine

  It determines what proteins the cell produces e.g haemoglobin. That in turn determines what type of cell it is e.g red blood cell
• What is genome?

  It is an entire set of genetic material in an organism.
• Why are determining the genes in the genome useful?

  It allows to link the gene with different types of disease. Knowing which genes are linked to the inherited diseases could help us understand them and develop effective treatments for them. Scientists can look at genomes to trace the migration of certain populations of people around the world. It can tell us when new populations split off in different direction and what route they took
• What is reproduction

  It is when genetic information in the chromosomes is passed on from parents to their offspring. There are two very different ways of reproducing asexual reproduction and sexual reproduction
• What is asexual reproduction


  This only involves one parent. The cells divide by mitosis. There is no joining (fusion) of special sex cells (gametes) and so there is no mixing of genetic information.
• What is there not in asexual reproduction

  There is no variation.
• What do asexual reproduction give a rise to

  It gives a rise to genetically identical offspring known as clones. Their genetic material is identical both to the parent and to each other. Only mitosis is involved in asexual reproduction
• What is asexual reproduction common in

  smallest animals and plants, and in fungi and bacteria. The cells of your body reproduce asexually all the time.
• What is mitosis.


  They divide into two identical cells
• What is sexual reproduction

  Is when genetic information from two organisms is combined to produce offspring which are genetically different to either parents. It is the fusion of two special sex cells to form a zygote, which goes on to develop a new individual.
• What is the difference between sexual reproduction and asexual

  In sexual reproduction, there is genetic variation, needs gametes, slow, more energy consuming, needs meiosis. While asexual is just one parents, produces clones, less energy consuming, quick
• How are gametes formed

  They're formed by meiosis. The chromosome number of the original cell is halved, so that when the gametes join together the cell has the right number of chromosomes.
• What does the offspring inherit

  It inherits genetic information from both parents. They will have some characteristics both parents, but won't be identical to either of them.
• How many chromosome does each gamete contain

  23 chromosomes, half the number of chromosomes in a normal cell. Instead of having two of each the gamete has just one.
• What are the gametes in plants

  The gametes are the egg cells and pollen
• Where does mitosis take place/what happens

  It takes place in tissues all over your body and whenever organism reproduce asexually. Before it divides it grows and increases sub cellular structure and duplicates it's DNA, so there's one coy for each. The chromosomes line up at the centre of the cell and the cell fibres pull them apart. Membranes form around each, the nucleus has divided. The cell has now produced two new daughter cells
• What is meiosis

  It is a type of cell division that takes place in the reproductive organs. It results in sex cells called gametes which only have half the original number of chromosomes
• What is the difference between meiosis and mitosis

  Mitosis results in 2 genetically same cells,while the results of meiosis are genetically different. Meiosis goes through two rounds of genetic separation while mitosis goes through one
• What happens in meiosis

  In meiosis, the chromosome number is reduced to a half in gametes. In a body cell there are two set of each chromosome, one inherited from the mother and one from the father. When a cell divides to form gamete. The genetic information is copied so there are four sets of each chromosome instead of two normal sets. Each chromosome forms a pair of chromatids. The cell than divides twice in quick succession to form four gametes each with a single set of chromosomes. Each gamete that is produced is genetically different from each other. Gametes contains random mixtures of the original chromosomes. This introduces variation.
• How does fertilisation add more variation?

  Each sex cell has a single set of chromosomes. When two sex cells join during fertilisation, the single new cell formed has a full set of chromosomes. In humans the egg cell has 23 chromosomes, and so does the sperm, when they join they produce a new body with 46 chromosomes in 23 pairs, the correct number of chromosomes for human body cells. The combination of genes on the chromosomes of every newly fertilised egg is unique. Once fertilisation is complete, the cells begin to divide by mitosis to form a new individual. As the embryo develops the cells differentiate to form different tissues, organs and organ systems.
• What are the disadvantages and advantages of asexual reproduction


  It can reproduce rapidly, producing identical offspring. This is advantage in favourable condition, but if environment changes disadvantage, if one organism can not survive none can. Asexual reproduction can be sped up by humans to reproduce large number of clones, for example by increasing food production.
• What are the advantages and disadvantages to sexual reproduction

  Two gametes are needed and it takes time and energy to find mate. It is slower. But produces variation, if environment changes, this variation gives a survival advantage as some offspring will be able to survive and reproduce. This is natural selection. Natural selection can be sped up by humans in selective breeding to increase food production. Selective breeding is where individuals with a desirable characteristics are bred to produce offspring
• What is common reproduction in fungi

  The most common form of reproduction is asexual. The moulds that rot our food are also reproduce asexually. Many fungi is made up of a mass of thin threads called hyphae that together form strucutres we can see. In asexual reproduction, the fungal spores are produced by mitosis and they are genetically identical to the parent.
• What do fungi sometimes do if conditions are bad

  They reproduce sexually if conditions aren't good, for example when it is too dry. Two hyphae from different fungi join and the nuclei fuse so the new hypha has two sets of chromosomes. It undergoes meiosis to make haploid spores, each with only one set of chromosomes, which are different from the original hyphae. Some of the spores may produce fungi better adapted to survive in the adverse conditions.
• What is reproduction in plants like

  In plants the flowers contain the organs of sexual reproduction. The gametes are produced via meiosis. The pollen from one flower must reach the female parts of another flower in a process called pollination. Flowers are adapted either to attract animal pollinators, such as insects, birds to make it easy for their pollen to be carried away by wind or caught by another flower. Once the pollen has fused with the egg cell, seeds are formed. Sexual reproduction introduces variation and enables them to survive through natural selection. Many plants also reproduce asexually. A new plant grows as a result of specially directed mitosis. Asexual reproduction means that the new plants are formed even if the flowers are destroyed. Main disadvantage is that the new plants are identical to their parents no variation. (runners and bulb division)
• What is reproduction in malaria parasites

  The parasites that cause malaria reproduce differently in different stages of their life cycle. Malarial parasites spend part of their life in the body of a female mosquito and part of their life cycle in the blood of human beings. Both asexual and sexual reproduction are part of it cycle. Malarial parasites reproduce asexually in human liver and blood cells. When the mosquito takes her blood meal, the drop in temperature between the human body and mosquito triggers sexual reproduction in some of the parasites inside the red blood cells. There is a 20 minute window when sexual forms develop burst out of the blood cells and meet to form zygotes with two sets of chromosomes. These zygotes then undergo meiosis to produce new asexual parasites that will infect a new human host. The parasites show a lot of variation. Mitosis alone in human, combination of meiosis and mitosis in the body of a female mosquito
• How many chromosomes do humans have

  46 chromosomes inherit half of your chromosomes from your mother and half from your father and found in 23 pairs
• What is the relationship between gene and whole organism

  It gives them the code of the particular sequence of amino acids to make specific protein. These proteins include enzymes that control your cell chemistry. These control and make up different specialised cells that form tissues. The tissues then form organ and organ systems that make up the whole body
• How are genome helpful in making us healthy

  It allows them to be sequenced, such as bacteria and viruses can be sequenced to help identify the cause. Furthermore we can have our genome sequenced to help us be sequenced
• What are DNA strands made up of

  DNA strands are polymers that are made up of lots of repeating units called nucleotides
• What are nucleotides consist of

  consists of one sugar molecule, one phosphate molecule and one base. The sugar and phosphate molecules form a backbone to the DNA strands. The sugar and phosphate molecules alternate. One of four different bases A , T ,C or G joins to each sugar. Each base links to a base on the opposite strand in the helix
• What does each base pair up with

  A always pairs up with T, and C always pairs up with G. This is called complementary base pairing.
• What does the order of amino acids in a protein depend on

  depend on the order of bases in a gene. Each amino acid is coded by a sequence of three bases in the gene. It is this particular sequence of amino acids that gives each protein a specific shape and function
• What is protein synthesis controlled by

  It is controlled by DNA in the nucleus