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Flashcards · 8461 · Topic 1
Cell biology flashcards
36 cards on Topic 1, subtopics 4.1.1 to 4.1.3. Pick a subtopic or study them all.
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4.1.1 Cell structure
- Eukaryotic vs prokaryotic cells
- Eukaryotic (plant and animal): larger, genetic material enclosed in a nucleus. Prokaryotic (bacteria): much smaller, a single DNA loop not in a nucleus, and may have plasmids. Both have a cell membrane and cytoplasm.
- Functions of the nucleus, cytoplasm, cell membrane, mitochondria and ribosomes
- Nucleus: genetic material that controls the cell. Cytoplasm: most chemical reactions. Cell membrane: controls what enters and leaves. Mitochondria: aerobic respiration. Ribosomes: protein synthesis.
- Three structures plant cells often have that animal cells do not
- Chloroplasts (absorb light for photosynthesis), a permanent vacuole filled with cell sap, and a cellulose cell wall that strengthens the cell.
- How are sperm, nerve and muscle cells adapted?
- Sperm: tail to swim; many mitochondria for energy. Nerve: long, to carry impulses a long way; branched endings to link to many cells. Muscle: protein fibres that contract; many mitochondria.
- How are root hair, xylem and phloem cells adapted?
- Root hair: long projection, large surface area to absorb water and mineral ions. Xylem: hollow tubes of dead cells strengthened by lignin. Phloem: end walls with pores so dissolved sugars pass from cell to cell.
- Cell differentiation in animals vs plants
- Differentiating cells gain the sub-cellular structures they need and become specialised. Most animal cells differentiate early; many plant cells keep the ability throughout life. In mature animals, cell division is mainly for repair and replacement.
- Light microscope vs electron microscope
- The electron microscope has a much higher magnification and resolution, so it shows many more sub-cellular structures in fine detail. Resolution is the ability to distinguish two close points as separate.
- An image is 12 mm wide; the real cell is 6 μm wide. Magnification?
- magnification = size of image ÷ size of real object. 12 mm = 12 000 μm, so 12 000 ÷ 6 = ×2000. Convert to the same unit first; magnification has no unit.
- Required practical 1: preparing and viewing a slide of onion cells
- Thin layer of cells on a slide; add iodine stain; lower a coverslip at an angle to avoid air bubbles; focus with the lowest-power objective first, then higher power with fine focus; pencil drawing with a scale bar.
- Culturing bacteria: aseptic steps and why school cultures are incubated at 25 °C
- Sterilise dishes and agar; flame the inoculating loop; tape the lid; store upside down. 25 °C reduces the chance of growing pathogens harmful to humans.
- Required practical 2: a clear zone around an antibiotic disc is 14 mm across. Its area?
- r = 7 mm. Area = πr² = π × 7² = 154 mm² (3 s.f.). A larger clear zone means a more effective antibiotic or antiseptic.
- 40 bacteria divide every 30 minutes. How many after 4 hours, in standard form?Higher
- 4 h = 240 min; 240 ÷ 30 = 8 divisions. 40 × 2⁸ = 10 240 = 1.024 × 10⁴ bacteria.
4.1.2 Cell division
- Chromosomes: where, what they are made of, and how arranged
- In the nucleus. Made of DNA molecules; each carries a large number of genes. In body cells they are normally found in pairs (23 pairs, 46 chromosomes, in humans).
- Cell cycle stage 1
- The cell grows, the number of sub-cellular structures (ribosomes, mitochondria) increases, and the DNA replicates to form two copies of each chromosome.
- Cell cycle stages 2 and 3
- Stage 2 (mitosis): one set of chromosomes is pulled to each end of the cell and the nucleus divides. Stage 3: the cytoplasm and cell membrane divide, forming two genetically identical cells.
- Why is mitosis important?
- Growth and development of multicellular organisms, repair and replacement of cells, and asexual reproduction (offspring are clones).
- Name two cases where cells divide but not by mitosis
- Making gametes (sperm and eggs), by meiosis; a bacterium dividing, by binary fission.
- A student counts 50 cells in a root tip and 4 are in mitosis. Percentage?
- 4 ÷ 50 × 100 = 8%.
- Stem cell
- An undifferentiated cell of an organism which can give rise to many more cells of the same type, and from which certain other cells can arise by differentiation.
- Stem cells from a human embryo vs adult bone marrow
- Embryonic: can become most types of human cell, and can be cloned and made to differentiate. Adult bone marrow: can form many types of cell, including blood cells.
- Meristem stem cells, and two uses of cloning plants from them
- Found at the tips of shoots and roots; can differentiate into any type of plant cell throughout the plant's life. Clones are made quickly and cheaply: to protect rare species from extinction, and to give many identical crop plants with useful features such as disease resistance.
- Therapeutic cloning
- An embryo is produced with the same genes as the patient. Its stem cells are not rejected by the patient's body, so they may be used for medical treatment.
- Possible benefits of stem cell treatment, and the risks and objections
- May be able to help conditions such as diabetes and paralysis. Risk: transfer of viral infection. Objection: some people have ethical or religious objections to using human embryos.
- Chromosome vs gene
- A chromosome is a long DNA molecule carrying many genes; a gene is one small section of that DNA.
4.1.3 Transport in cells
- Diffusion
- The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.
- Osmosis
- The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
- Active transport
- Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). It requires energy from respiration.
- Two examples of diffusion named in the specification
- Oxygen and carbon dioxide in gas exchange; urea from cells into the blood plasma, for excretion in the kidney.
- Three factors that increase the rate of diffusion
- A steeper concentration gradient, a higher temperature (particles move faster), and a larger membrane surface area.
- Surface area to volume ratio of a cube of side 3 cm
- SA = 6 × 3² = 54 cm²; V = 3³ = 27 cm³; ratio = 54 ÷ 27 = 2 : 1. A cube of side 0.5 cm has 12 : 1, so smaller objects have larger ratios.
- Why do multicellular organisms need exchange surfaces and a transport system?
- They have a small surface area to volume ratio, so the outer surface is too small for their needs and inner cells are too far away for diffusion alone.
- Four features that make an exchange surface effective
- A large surface area; a thin membrane (short diffusion path); an efficient blood supply (animals); ventilation (animals, for gas exchange). The last two keep the concentration gradient steep.
- Required practical 3: method and variables
- Cut equal cylinders of potato, blot and weigh; put each in a different concentration of salt or sugar solution for the same time; blot and reweigh. Independent: concentration. Dependent: percentage change in mass. Control: size, volume, time, temperature.
- Potato tissue goes from 1.60 g to 1.84 g. Percentage change in mass?
- (1.84 − 1.60) ÷ 1.60 × 100 = +15%. Always divide by the initial mass and keep the sign.
- On a graph of percentage change in mass against concentration, what does the x-intercept show?
- The concentration with no net movement of water, which is the same as the concentration of the cell contents.
- Two examples of active transport
- Plants: mineral ions absorbed into root hair cells from very dilute soil solution. Animals: sugar absorbed from the gut into the blood, where its concentration is higher.