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KS4 Cells Division & Reproduction
- Know that the nucleus of a cell contains chromosomes made of DNA molecules.
- Know that each chromosome carries a large number of genes.
- Know that in body cells the chromosomes are normally found in pairs.
1.2.2 Mitosis and the cell cycle
- Know that cells divide in a series of stages called the cell cycle and that one of these stages is mitosis where the DNA, which has already been copied, divides.
- Know that during the cell cycle the genetic material is doubled and then divided into two identical cells.
- Know that before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria.
- Know that the DNA replicates to form two copies of each chromosome and that one set of chromosomes is pulled to each end of the cell and the nucleus divides.
- Know that at the end of the cell cycle the cytoplasm and cell membranes divide to form two identical cells. (Knowledge of the stages of mitosis is not required)
- Know that Cell division by mitosis is important in the growth and development of multicellular organisms.
- Be able to recognise and describe situations in given contexts where mitosis is occurring.
1.2.3 Stem Cells
- Know that a stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.
- Know that stem cells from human embryos can be cloned and made to differentiate into many different types of human cells. (Knowledge and understanding of stem cell techniques are not required).
- Know that stem cells from and adult bone marrow can form many types of cells including blood cells
- Know that meristems in plants can differentiate into any type of plant cell, throughout the life of the plant.
- Know that treatment with stem cells may be able to help conditions such as diabetes and paralysis.
- Know that in therapeutic cloning an embryo is produced with the same genes as the patient.
- Know that stem cells from the embryo are not rejected by the patient’s body so they may be used for medical treatment.
- Know that the use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections.
- Know that stem cells from meristems in plants can be used to produce clones of plants quickly and economically, eg Rare species can be cloned to protect from extinction or large numbers of identical crop plants with special features such as disease resistance
- Be able to evaluate the practical risks and benefits, as well as social and ethical issues, of the use of stem cells in medical research and treatments.
6.1.1 Sexual and asexual reproduction
- Know that meiosis leads to non-identical cells being formed while mitosis leads to identical cells being formed.
- Know that sexual reproduction involves the joining (fusion) of male and female gametes: sperm and egg cells in animals and pollen and egg cells in flowering plants.
- Know that in sexual reproduction there is mixing of genetic information which leads to variety in the offspring.
- Know that the formation of gametes involves meiosis.
- Know that asexual reproduction involves only one parent and no fusion of gametes.
- Know that in asexual reproduction there is no mixing of genetic information and that this leads to genetically identical offspring (clones).
6.1.2 Meiosis (NB: Knowledge of the stages of meiosis is not required.)
- Be able to explain how meiosis halves the number of chromosomes in gametes and fertilisation restores the full number of chromosomes.
- Know that cells in reproductive organs divide by meiosis to form gametes.
- Know that when a cell divides to form gametes:
- copies of the genetic information are made
- the cell divides twice to form four gametes, each with a single set of chromosomes
- all gametes are genetically different from each other.
- Know that gametes join at fertilisation to restore the normal number of chromosomes.
- Know that the new cell formed at fertilisation divides by mitosis increasing the number of cells.
- Know that as the embryo develops cells differentiate.
6.1.3 Advantages and disadvantages of sexual and asexual reproduction
- Know the advantages of sexual reproduction include:
- produces variation in the offspring
- if the environment changes variation gives a survival advantage by natural selection
- natural selection can be speeded up by humans in selective breeding to increase food production.
- Advantages of asexual reproduction include:
- only one parent needed
- more time and energy efficient as do not need to find a mate
- faster than sexual reproduction
- many identical offspring can be produced when conditions are favourable.
- Know that some organisms reproduce by both methods depending on the circumstances.
- Know that malarial parasites reproduce asexually in the human host, but sexually in the mosquito.
- Know the historical developments of our understanding of the causes and prevention of malaria.
- Know that many fungi reproduce asexually by spores but also reproduce sexually to give variation.
- Know that many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.
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