cell biology

• Eukaryotic cells contain their genetic material (DNA) enclosed in a nucleus.
• animal and plant cells both have a nucleus, a cell membrane, cytoplasm and ribosomes
• a bacterial cell is a prokaryote. In prokaryotic cells, the genetic material is not enclosed in a nucleus.
• prokaryotic cells are much smaller than eukaryotic cells.
• the genetic material in a prokaryotic cell consists of a single loop of dna, there may also be rings of dna which are called plasmids.
• prokaryotic cells have a cell membrane, a cell wall, cytoplasm and a loop of dna and plasmids.
• 1m = 100cm = 1,000mm = 1,000,000 µm (micrometer) = 1,000,000,000 nm (nanometers)
• a typical human cell is around 10-20 µm
• a molecule of the protein haemoglobin is 5nm (nanometers)
• 1 order of magnitude means 10x.
• 1 order of magnitude means 10x. for example a pineapple is 10x bigger than a lemon so the pineapple is 1 order of magnitude larger than the lemon.
• a dog is 100x longer than a spider, therefore the dog is 2 orders of magnitude longer than the spider.
• by counting the zeros it tells you the order of magnitude.

  10x bigger = 1 order of magnitude

  100x bigger = 2 orders of magnitude
• animals are eukaryotic. Their genetic material is enclosed in a nucleus.
• the function of the nucleus is to enclose the genetic material
• the cytoplasm is a watery solution where chemical reactions take place.
• the cell membrane controls the molecules that can enter and leave the cell.
• mitochondria and ribosomes are found in the cytoplasm of a cell
• mitochondria are where aerobic respiration takes place
• ribosomes are extremely small so we cant see them using a light microscope, instead we need to use a much more powerful microscope called an electron microscope.
• ribosomes are the sights of protein synthesis
• an animal cell contains a nucleus, a cell membrane, cytoplasm, mitochondria and ribosomes
• plant cells have a regular shape, unlike animal cells which can easily change their shape
• plant cells contain a nucleus, cytoplasm, cell membrane, mitochondria, ribosomes, chloroplasts, vacuole and a cell wall.
• chloroplasts contain chlorophyll and are the sites of photosynthesis
• the cell wall is made from cellulose. This strengthens the cell.
• the vacuole is filled with a fluid called cell sap. It also gives the plant its shape.
• animal cells that are specialised to carry out functions are: sperm cells, nerve cells and muscle cells.
• most animal cells are specialised - they've got adaptations which help them carry out their functions.
• when cells become specialised, scientists call that differentiation
• the job of a sperm cell is to join with an ovum (an egg cell). We call this fertilisation. During fertilisation, the genetic information of the ovum and the sperm, combine. Sperm cells have a long tail which allows them to swim to the ovum. They are also streamlined to make this easier. Sperm cells are packed full of mitochondria. These provide the energy needed for swimming. Sperm cells also contain enzymes, which allow them to digest their way through the outer layer of the ovum.
• the job of a nerve cell is to send electrical impulses around the body. Nerve cells have a long axon. The axon carries the electrical impulses from one part of the body to another. The axon is covered in myelin which insulates the axon and speeds up the transmission of nerve impulses. The end of the axon has synapses, synapses are junctions which allow the impulse to pass from one nerve cell to another (a small gap that separates neurones). The cell body of the nerve cell has dendrites, which increase the surface area so that other nerve cells can connect more easily.

  
• muscle cells can contract (get shorter). to do this muscle cells contain protein fibres whihc can change their length. When a muscle cell contracts, these protein fibres shorten. muscle cells are also packed full of mitochondria to provide energy for muscle contraction. muscle cells work together to form muscle tissue
• most plant cells are specialised.
• the plant cells which are specialised are: root hair cells, xylem cells and phloem cells
• the hairs on a root increase the surface area of the root, so it can absorb water, dissolved minerals and nitrate ions more effectively. These hairs are formed on root hair cells. Root hair cells are underground therefore they dont get energy from the sun therefore they dont have chloroplasts.
• xylem are found in the plant stem and they form long tubes. These tubes carry water and dissolved minerals from the roots to the leaves. xylem cells have very thick walls, containing lignin. This provides support to the plant. Because the cell walls are sealed with lignin, this causes the xylem cells to die. The end walls between the cells have now completely broken down, this means the cells can now form a long tube so water and dissolved minerals can flow easily. Xylem cells have no internal structures at all. That makes it easier for water and minerals to flow.
• Phloem tubes carry dissolved sugars up and down the plant. Phloem vessel cells (have no nucleus and limited cytoplasm). The end walls of the vessel cells have pores called sieve plates, both of these features allow dissolved sugars to move through the cell interior. Because phloem vessel cells have got very limited cytoplasm - they haven't got many mitochondria. Therefore they each have a companion cell connected by pores. Mitochondria in the companion cell provide energy to the phloem vessel cell.
• light microscopes:

  • use light to view the specimen
  • limited magnification
  • limited resolution
• magnifying = making something bigger