Cell Biology

• Both animal and plant cells are EUKARYOTIC, meaning that all of their genetic material (DNA) is enclosed within a nucleus.
• Animal cells contain a nucleus (which contain all of their genetic material), a cell membrane, and a cytoplasm.
• PROKARYOTIC cells are cells in which the genetic material is not enclosed within a nucleus. E.g bacterial cells contain a single loop of DNA, sometimes, they also contain small plasmids (small loops of DNA). They have a bacterial cell wall, a cell membrane, and a cytoplasm.
• PROKARYOTIC cells are much smaller than EUKARYOTIC cells.
• 1 metre - 1 000 000 micrometres
• 1 nanometre - 1 billionth of a metre
• 1 order of magnitude = 10x e.g a pineapple is 1 order of magnitude larger than a lemon, it is 10x larger than a lemon.
• Every order of magnitude is 10x greater than the one before. 2 orders of magnitude greater = 100x larger.
• The function of the nucleus is to enclose the genetic material of the cell.
• Within the cytoplasm, chemical reactions take place e.g the first stage of respiration.
• The whole cell is enclosed in a cell membrane (animal cells), which controls the molecules that can leave and enter the cell.
• Mitochondria are where aerobic respiration takes place.
• Ribosomes are the sites of protein synthesis in the cell.
• Plant cells have a regular shape.
• Both PLANT CELLS and ANIMAL CELLS contain: Cell membrane, Cytoplasm, Nucleus, Mitochondria and Ribosomes.
• Chloroplasts contain chlorophyll and are the sites of photosynthesis.
• The cell wall is made from cellulose which strengthens the cell and provides support.
• The permanent vacuole is filled with cell sap. The vacuole helps give the cell its shape.
• Most animal cells are specialised - They have adaptations which help them carry out their particular function. When cells become specialised, it is called differentiation.
• The job of the sperm cell is to join with an ovum (egg cell). This process is called fertilisation. During fertilisation, the genetic information of the ovum and the sperm cell combine.
• Sperm cells contain their genetic information in the nucleus. However, sperm cells only contain half the genetic information of a normal adult cell.
• Sperm cells have a long tail which allows them to swim to the ovum, they also have a streamlined shape to make this easier.
• Sperm cells are packed full of mitochondria, which provide the energy needed for swimming.
• Sperm cells 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. They have a long axon. The axon carries the electrical impulses from one part of the body to another.
• On a nerve cell, the axon is covered with a myelin sheath which insulates the axon and speeds up the transmission of nerve impulses
• On a nerve cell, the end of the axon has synapses. Synapses are junctions which allow the impulse to pass from one nerve cell to another.
• 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 and to do this they contain protein fibres which can change their length. When a muscle cell contracts, the protein fibres shorten and the muscle cell becomes tighter, decreasing the length of the cell.
• Muscle cells are also packed full of mitochondria to provide energy for muscle contraction.
• Muscle cells work together to form muscle tissue.
• Root hair cells have root hair which increase the surface area of the root, so it can absorb water and dissolved minerals more effectively. Root hair cells do not contain chloroplasts as they are underground and therefore cannot carry out photosynthesis.
• Xylem are found in a 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, which 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 broken down, meaning that the cells now form a long tube so water and dissolved minerals can flow easily. Xylem cells also have no internal structures, making it easier for things to flow.
• Phloem tubes carry dissolved sugars up and down the plant. Phloem vessel cells have no nucleus and only limited cytoplasm. The end walls of the vessel cells have pores called sieve plates. Both of these features allow dissolves sugars to move through the cell interior. Because phloem vessel cells have very limited cytoplasm, they haven't got many mitochondria, so each phloem vessel cell has a companion cell connected by pores. Mitochondria in the companion cell provide energy to the phloem vessel cell.
• The centre of an optical microscope has a stage, where we place the microscope slide. The stage has clips to hold the slide in place. Below the stage is a lamp, light from the lamp passes up through the microscope slide. Above the stage are the objective lenses which usually have a magnification of 4x, 10x or 40x. At the top of the microscope is the eyepiece where we look through, it contains the eyepiece lens, which has a magnification of 10x. The coarse focussing dial moves the stage up and down, the fine focussing dial brings the cells into a clear focus.
• Light microscopes have a limited magnification and a limited resolution. Electron microscopes have a much greater magnification and resolution. Magnification = image size / actual size
• A specimen must be prepared properly if we want to see its structure clearly using a light microscope. We need to stain the specimen to make the different parts visible. Staining involves adding dyes to the specimen. Different stains bind to different components within the cell. Some stains will bind to DNA, others will bind to proteins etc. This allows us to distinguish one part of the cell from another.
• bacteria multiply by simple cell division, one bacterial cell splits into two bacterial cells (binary fission). Bacteria can carry out binary fission once every 20 minutes as long as they have enough nutrients and the temperature is suitable.
• number of bacteria = 2^n, n is the number of rounds of division.
• Bacteria reproduce quickly because there is little time between divisions. They also don't require any specialised structures like spores, so they can divide more often than other organisms.