Cells

• Animal cells become specialised early in development and these cells can only divide by mitosis to create two identical daughter cells.
• Plant cells can become specialised throughout their life time. Undifferentiated cells form at growing areas of plants called meristems. Meristem cells grow and then differentiate at their final positions.
• Mitosis:

  First stage- a normal cell has 46 chromosomes/ 23 pairs, organelle numbers double

  Second stage- a set of chromosomes are pulled to one side of the cell and the nucleus divides

  Third stage- cytoplasm and cell membrane divide (cytokinesis) to form 2 genetically identical daughter cells
• Stem cells are undifferentiated and can become any type of cell. There are two types: adult stem cells and embryonic stem cells.
• Everytime a stem cell divides, it either produces another stem cell or a specialised cell.
• Adult stem cells:

  Most are not fully specialised

  Good source is found in bone marrow

  Can differentiate to form all blood cells but can form others, like brain or muscle.
• Nerve cells- transmit electrical signals/impulses. Have long, thin bodies with projections
• Sperm cell- carries father’s DNA, used to fertilise an egg, have no nucleus, has enzymes on the tip, has lots of mitochondria and has a tail to swim.
• Muscle cell- used to allow movement, they contract and expand
• Red blood cell- carries oxygen around the body. They have no nucleus.
• Guard cell- inside leaves. They open and close the stomata and control how much light comes in and out of the cell.
• Root hair cell- absorbs as much water and minerals as possible. Has large surface area for efficient gas exchange.
• Xylem- carries water and minerals. Unidirectional.
• Phloem- carries sugars around the plant bidirectionally.
• Palisade cell- where photosynthesis occurs. Has chloroplasts for as much photosynthesis as possible.
• Eukaryotic cells- younger cells. 10 micrometers. Found in animal and plant cells. They have a nucleus, mitochondria, ribosomes and a cell membrane.
• Prokaryotic cells are older cells. They are 1 micrometer big. They are found in bacteria. They have a slime capsule, flagella, cell wall, cell membrane, cytoplasm, plasmids and genetic material.
• Plant cells have:

  Vacuole- contains cell sap

  Chloroplasts- for photosynthesis

  Ribosomes- for protein synthesis

  Cell wall- extra protection, keeps shape of cell

  Cell membrane- controls what comes into and out of the cell

  Mitochondria- where respiration occurs

  Nucleus-contains DNA, controls cell activity

  Cytoplasm-where chemical reactions take place
• Animal cells have:

  Nucleus-contains DNA, controls cell activity

  Cell membrane- controls what comes into and out of the cell

  Mitochondria- where cell respiration takes place

  Ribosome-where protein synthesis occurs

  Cytoplasm-where chemical reactions take place
• Embryonic stem cells can become any type of cell and are completely undifferentiated.
• Adult stem cells can only become one/ that type of stem cell.
• Magnification= size of image / actual size
• Xylem cells are walls of dead cells, strengthened by lignin. They also have no end walls to allow for water and mineral ions to flow easily throughout the plant.
• Phloem cells have sieve plates or pores which allow for solutions to move through the cells.
• Light microscopes are cheaper, easier to use but have a lower resolution than electron microscopes.