Biology - Unit 2 Topic 3

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  1. Describe the ultrastructure of the nucleus and the nucleolus.
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    • The nucleus has a double membrane with pores.
    • It contains chromatin and a nucleolus.
    • Nucleolus makes ribosomes.
    • Chromatin contains DNA and controls protein synthesis.
  2. Describe the ultrastructure of a ribosome.
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    • Made of RNA and protein.
    • They are found free in the cytoplasm or attached to the RER.
    • Site of protein synthesis.
  3. Describe the ultrastructure of SER and RER.
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    • RER:
    • Interconnected sacs embedded with ribosomes.
    • Site of protein folding and processing proteins.
    • SER:
    • Interconnected sacs where synthesis of lipids and steroids occurs.
  4. Describe the ultrastructure of a mitochondria.
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    • Enclosed by a double membrane.
    • The inner membrane is folded into cristae.
    • The inner membrane is filled with the matrix.
    • Its the site of aerobic respiration where ATP is produced.
  5. Describe the ultrastructure of centrioles.
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    • Animal cells contain a pair.
    • The are hollow cylinders containing a ring of microtubules.
    • The are involved in spindle formation for cell division.
  6. Describe the ultrastructure of a lysosome.
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    • Round organelle surrounded by a membrane containing digestive enzymes.
    • Used to digest unwanted structures or old cells.
  7. Describe the ultrastructure of the golgi apparatus.
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    • Group of fluid filled flattened sacs, vesicles seen next to it.
    • Processes and packages new lipids and proteins, and makes lysosomes.
  8. Explain the role of the RER and the Golgi apparatus.
    • Proteins are synthesised in ribosomes which are held at RER.
    • Proteins are folded in the RER.
    • These proteins are then released in vesicles and fuse with the Golgi apparatus.
    • Proteins are modified in the Golgi, e.g. given receptors (glycoproteins).
    • The Golgi also produces lysosomes.
    • Vesicles full of enzymes move towards the cell surface membrane and leave the Golgi by exocytosis.
  9. Distinguish between eukaryotic and prokaryotic cells.
    • Eukaryotes:
    • Larger.
    • Have linear DNA.
    • Have a nucleus.
    • Either have no cell wall, a cellulose cell wall or a chitin cell wall.
    • Contain many organelles, including mitochondria.
    • Larger ribosomes.

    • Prokaryotes:
    • Very small.
    • Circular DNA.
    • No nucleus. (Has plasmids)
    • Cell wall made of polysaccharide.
    • Few organelles and no mitochondria.
    • Smaller ribosomes.
  10. Describe the terms tissue, organ and system.
    • A tissue is on or more similar cell types working together to execute the same function.
    • An organ is a group of similar tissues working together to execute several functions.
    • A system is a group of organs working together to execute a function.
  11. Explain the role of mitosis and the cell cycle.
    • Mitosis is used for growth, repair and asexual reproduction.
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    • Prophase:
    • Chromatids become visible.
    • Centrioles move to opposite poles.
    • Nucleolus disappears and nuclear envelope breaks down.
    • Spindle begins to form.
    • Metaphase:
    • Chromosomes line up at equator and are attached to the spindle by their centromere.
    • Anaphase:
    • Centromeres divide.
    • Spindles contract pulling chromatids to opposite poles.
    • Telophase:
    • Spindle breaks down.
    • Chromosomes de condense.
    • Nuclear envelope and nucleolus reform.
    • Cytoplasm splits forming two identical cells.
    • Cytokinesis:
    • Cytoplasmic division of two daughter cells.
  12. Root tip squash mitosis practical.
    • 1. Cut a 5mm tip from a growing root.
    • 2. Place root on a watch glass and then add HCl.
    • 3. Add a few drops of stain (toluidine blue) to darken the chromosomes and make them visible.
    • 4. Warm the watch glass using a Bunsen burner.
    • 5. Place the root tip on a microscope slide and squash it with a cover slip.
    • 6. Warm gently again to intensify stain.
    • 7. Repeat experiment to increase reliability.
  13. Explain meiosis and how it contributes to genetic variation.
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    • Cell division by meiosis produces gametes.
    • Meiosis produces haploid nuclei which are restored to diploid at fertilisation.
    • 1. DNA replicated into two sister chromatids.
    • 2. Homologous pairs line up along the equator.
    • 3. There is cross-over of chromatids before first division. This recombines genetic material and means chromatids now have different combination of alleles. 4 daughter cells will have different combination of alleles.
    • 4. At the first division, the homologous pairs are separated by independent assortment and the chromosome no. is halved.
    • 5. In the second (mitotic) division the sister chromatids are separated, resulting in a 4 unique haploid daughter cells.
  14. Explain how mammalian gametes are specialised for their function.
    • Sperm cell:
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    • Streamlined shape to reduce resistance.
    • Acrosome containing digestive enzymes (acrosin) to break down zona pellucida.
    • Haploid nucleus, which becomes diploid at fertilisation.
    • Many mitochondria to provide ATP for sperm to swim.
    • Flagellum to swim.
    • Receptors in cell surface membrane to bind to egg cell surface membrane.
    • Egg cell:
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    • Follicle cells form protective coating.
    • Much larger cell, containing food supply.
    • Contains zona pellucida which hardens after sperm enters.
  15. Describe the process of fertilisation in mammals and the importance of fertilisation.
    • Fertilisation occurs in the oviduct.
    • When sperm makes contact with zona pellucida acrosome reaction occurs.
    • Acrosin is released from the acrosome and digests the zone pellucida.
    • When sperm head reaches the egg cell membrane and it fuses, the cortical reaction is triggered.
    • Egg cell releases cortical granules which thicken and harden the zone pellucida making it impenetrable.
    • The sperm cell nucleus enters the egg cell and the tail is discarded.
    • The two nuclei fuse forming a diploid zygote.
  16. Describe the process of fertilisation in flowering plants.
    • Pollen grain lands on the stigma.
    • Grain absorbs water and splits open, releasing the tube cell which digests a pollen tube down the style.
    • The pollen tube transports the male generative cell (two haploid male gametes).
    • The pollen tube grows through the micropyle and into the embryo sac.
    • Tube nucleus disintegrates and the two haploid male nuclei enter the embryo sac.
    • One nucleus fuses with the egg cell to form a zygote and the other with the polar nuclei to form a triploid endosperm which will be used as a food source.
    • Double fertilisation has occured.
  17. Explain the terms stem cell, pluripotency, multi potency and totipotency.
    • Stem cell:
    • Unspecialised cells, found in an embryo or in the bone marrow.
    • Pluripotency:
    • Are stem cells that have the ability to differentiate into any cell except extra embryonic cells.
    • Found in the blastocyst.
    • Totipotency:
    • Stem cells that have the ability to differentiate into any cell including extra embryonic cells.
    • No genes are switched off. Found in 1-3 day old embryos.
    • Multipotent:
    • Stem cells in adult human tissue which can differentiate into a very few select number of cells, e.g. fetal tissue, cord blood, adult stem cells.
  18. How do cells become specialised?
    • Stem cells all contain the same genes but not all of them are expressed/active.
    • Under the right conditions some genes in stem cells are activated.
    • mRNA is only transcribed form the active genes.
    • mRNA from active genes is then translated into proteins.
    • Proteins modify the cell - control cell structure and processes.
    • These modifications cause the cell to become differentiated/specialised.
  19. What are the benefits of using stem cell therapies?
    • You can replaced damaged tissue, e.g. nerve tissue for spinal chord diseases, cardiac tissue for heart diseases.
    • Save lives, e.g. growing organs for transplants.
    • Quality of life is improved, e.g. replacing damaged cells in blind people.
  20. How do we obtain stem cells?
    • Adult stem cells:
    • Obtained from the bone marrow.
    • Operation can cause discomfort.
    • A needle is inserted into the centre of the bone and bone marrow removed.
    • Adult stem cells are very limited, therefore not very useful.
    • Embryonic stem cells:
    • Obtained from unused early embryos from IVF.
    • Stem cells are removed after 4-5 days and the embryo is then destroyed.
    • These stem cells are totipotent until blastocyst phase and after are pluripotent - much more useful.
    • But they are more likely to cause immune rejection than adult stem cells.
  21. What are the issues with stem cells therapies and who makes the decisions?
    • ☒It is unethical to destroy and embryo which could give rise to a human life. (Right to life)
    • ☑Less objections to stem cells from unfertilised embryos.
    • ☑Adult stem cell use requires no destruction of embryos.
    • ☒Adult stem cells are limited in use.
    • The regulatory authority looks at proposals of stem cell research and decides if it should be allowed.
    • Licensing/monitoring centres ensure only fully trained staff are carrying out procedures.
    • Guidelines and codes of practice to ensure scientists are working in a similar manner.
    • Developments in research and advances are monitored to ensure everything is up-to-date.
    • Information and advice is provided to help society understand how embryonic research works.
  22. Describe how totipotency can be demonstrated practically using plant tissue culture techniques.
    • 1. A single cell is taken from a growing area e.g. root.
    • 2. Place cell in a sterile growth medium (agar).
    • 3. The growth medium should contain nutrients and growth hormones.
    • 4. The plant cell will grow into unspecialised cells which will then differentiate into specialised cells in optimum conditions.
    • 5. Eventually cells will grow and differentiate into an entire plant.
  23. Explain how phenotype is the result of an interaction between genotype and the environment.
    • Animal hair colour:
    • Some animals have fur colour that is product of the environment. 
    • E.g. Siamese cats should have dark fur.
    • Genotype codes for dark fur.
    • Enzymes denatured by body heat so phenotype is affected by environment.
    • MAOA:
    • Enzyme that breaks down monoamines.
    • MAOA is monogenic (controlled by single gene).
    • But environmental factors like antidepressants and tobacco can reduce MAOA production.
    • Low levels of MAOA can lead to mental health problems.
    • Cancer:
    • Tumour occurs by mutation in cell division controllers (oncogenes, tumour suppressor genes).
    • Tumours can also occur by natural mutations caused by radiation, free radicals and carcinogen chemicals.
    • Human height:
    • Controlled by many genes (polygenic inheritance).
    • Also largely affected by environment (diet, sports).
  24. Explain continuous and discontinuous variation, epistasis and locus.
    • Continuous variation:
    • Phenotypes appear in a range of values (height).
    • Caused by many genes at different loci (polygenic) where environment has large effect.
    • Discontinuous variation:
    • Phenotypes appear in discrete categories (sex, blood group).
    • Controlled by one gene where environment has little effect.
    • Epistasis:
    • In polygenic traits some genes sometimes suppress others. 
    • E.g. bald gene suppresses blonde or red hair gene.
    • Locus:
    • Different alleles for the same gene are formed in the same position on chromosomes which are called the locus.
Card Set:
Biology - Unit 2 Topic 3
2015-04-13 15:12:51
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