cell biology

• living organisms are made up of one or more cells these include: plant animal and bacteria
• cell theory states that all living things are composed of one or more cells, the cell is the basic unit of structure and function in an organism, new cells arise only from existing cells.
• plant and animal cells are about 10-100 micrometers across. a micrometer is a thousandth of a millimeter
• bacteria cells are usually 0.5-5 micrometers across
• eukaryotes are organisms whose cells have a nucleus and membrane bound organelles
• plant and animal cells are eukaryotes because they have a nucleus
• animal cells 


  cell membrane that decides what enters and exits the cell. cytoplasm where chemical reactions take place due to it containing enzymes. a nucleus which controls cell activity. mitochondria where respiration occurs. ribosomes manufacture the proteins the cell needs
• plant cell

  cell wall made of cellulose strengthens the cell. chloroplasts are where photosynthesis occur ( are green because they contain chlorophyll). the permeant vacuole contains sell sap, a weak solution of salts and sugar that helps to support cell shape
• prokaryotic cells are organisms whose cells don't contain a nucleus or other organelles
• bacteria cells

  they don't have a nucleus, consist of cytoplasm surrounded by cell membrane and wall. genetic material consists of single loop of DNA that sits in cytoplasm. May also contain 1 or more plasmids ( circular DNA molecules).
• muscle cells

  are adapted to contract, are shaped as long tubes and contain large amounts of mitochondria to provide energy
• nerve cells

  are specialized to send signals called impulses, they are long in order to send electrical signals around the body they have branches (dendrites) that connect with muscles, glands and other nerves
• sperm cell

  is used to carry male DNA to female DNA in the egg, it has a long flexible tail that allows it to swim, large number of mitochondria in the middle section to provide energy, the head carries enzymes and these enzymes help the sperm break through the membrane of the egg
• root hair

  are adapted to absorb water and mineral ions. root hair cells take in water and nutrients from the soil, they are long and thin which gives them a large surface area. which makes it easier to absorb water and nutrients
• xylem

  xylem tissue transport water up the plant, the cells are hollow tubes reinforced with lignin for strength.
• phloem

  phloem tissue transports sugar up and down the plant, phloem tissue has elongated cells that are adapted to transport food molecules, the sugar molecules pass through one cell to the next through pores in their end walls
• animal cells only specialize for replacement and repair however man plant cells don't loose the ability to differentiate
• stem cells can differentiate and are either adult or embryonic
• adult stem cells can differentiate into a particular type of cell e.g. bone marrow, blood cells and immune cells
• an embryotic stem cell can turn into any type of cell as it need to differentiate into all the organisms different cells
• stem cells can be used to grow new tissue or repair damaged organs and can be used to treat paralyzed patients or people with diabetes.
• embryonic stem cells can be used for therapeutic cloning. it wont be rejected by the patient as it has the same genetic material
• stem cells have potential medical risks e.g. viruses can infect stem cells which could be transferred into a patient. people may also appose on ethical and religious backgrounds as they believe it is wrong to use human embryos as embryonic stem cells is also a potential human life
• cells in meristems are able to differentiate into any type of cell. this allows cloning to happen quickly and cheaply
• plant cloning can prevent endangered plants from extinction and can make disease resistant plants, this can be helpful to farmers who want large numbers of identical plants
• light microscopes use lenses to focus light and create magnified images. they include an eyepiece, rough and focus lenses, and objective lenses a specimen slide an a nosepiece
• light microscopes have a limited resolution Resolution - the ability to distinguish between points close together
• electron microscopes use a beam of electrons passing through the sample to form an image, an electron is a tiny negatively charged particle they have a much higher resolution and magnification
• magnification = image size/real size
• the nucleus contains chromosomes which carry genetic material, they usually come in pairs and have long strands of DNA containing thousands of genes ( a gene is a section of DNA that has info to make a specific protein)
• cell division creates new cells these new cells allow the organism to grow, new cells are also needed to replace old or damaged cells
• mitosis

  in the cell cycle two identical cells are formed from one stage 1: cell grows larger increasing number of mitochondria and ribosomes stage 2: chromosomes replicate creating two copies stage 3: the cell is divided into two
• particles in liquids and gases move about randomly they move from areas of high concentration to areas of low concentration this is called diffusion
• particles diffuse in and out of our cell through the membrane e.g. the alveoli is surrounded by capillaries which have low concentration of oxygen, so oxygen has to diffuse from the alveoli to the blood
• another example of diffusion is the movement of urea. it diffuses out of the cells into the blood plasma as urea is small enough to pass through the cell membrane and there is a higher concentration in the body cells than in blood
• rate affecting diffusion: concentration gradient, temperature, surface area, partial pressure of the gas
• volume = height x width x depth
• single-celled organisms have a very large surface area compared to their volume this means molecules can easily diffuse in and out of the cell
• singled-celled organisms have a very large surface area compered to their volume this allows molecules to easily diffuse in and out of the cell
• multicellular organisms have a small surface area to volume ratio so they have specialized structures for exchanging materials and to increase rate of diffusion. this can be done through: having a thin membrane, being well ventilated and having a larger concentration gradient