Cell biology flashcards

Key points

• Animal and plant cells are eukaryotic: their DNA is inside a nucleus.
• Bacteria are prokaryotic: much smaller, with no nucleus.
• A bacterium's DNA is a single loop in the cytoplasm, often with small extra rings called plasmids.
• Bacteria have a cell membrane, cytoplasm, ribosomes and a cell wall.

Key points

• Nucleus: holds the DNA and controls the cell.
• Cytoplasm: where most reactions happen. Cell membrane: controls what goes in and out.
• Mitochondria: aerobic respiration releases energy. Ribosomes: make proteins.
• Plant cells add a cellulose cell wall, a permanent vacuole and chloroplasts for photosynthesis.

Key points

• An electron microscope has a much higher magnification and resolution.
• Resolution is how well two points close together can be told apart.
• So it shows tiny structures, such as ribosomes and the inside of mitochondria.
• A light microscope is cheap and portable, and can look at living cells.

Key points

• Put both sizes in the same unit before you divide.
• 1 mm = 1000 µm.

Formulae

Image 12 mm, real size 20 µm

Key points

• First the cell grows, copies its DNA and makes more sub-cellular structures.
• In mitosis the two sets of chromosomes are pulled to opposite ends of the cell.
• Then the cytoplasm and membrane divide to make two cells.
• The two cells are genetically identical to the parent, for growth and repair.

Key points

• Stem cells are undifferentiated: they can divide and become specialised cells.
• Embryonic stem cells can become almost any cell; adult ones (in bone marrow) only a few types.
• In plants they are in the meristems, at the tips of roots and shoots.
• They could replace damaged cells, but using embryos raises ethical concerns.

Key points

• Diffusion: particles spread from a higher to a lower concentration. It needs no energy.
• Osmosis: water moves from a dilute solution to a more concentrated one.
• Osmosis only happens through a partially permeable membrane.
• Faster with a steeper concentration gradient, a higher temperature and a bigger surface area.

Key points

• It moves substances from a dilute solution to a more concentrated one.
• That is against the concentration gradient, so it needs energy from respiration.
• Root hair cells take in mineral ions this way, because the soil is more dilute than the cell.
• Water still enters the root hair cell by osmosis.

Key points

• As an organism gets bigger, its surface area to volume ratio gets smaller.
• Its outside surface is then too small for diffusion to supply every cell.
• So exchange surfaces have a large surface area, thin walls and a good blood supply.

A cube with 2 cm sides