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Biology (Cell biology (Cell structure, Transport in cells (Explain how the…

- - - - Stem cells are a class of undifferentiated cells that are able to differentiate into specialized cell types.
      - An early animal embryo contains stem cells that have the potential to divide and develop into any type of specialised body cell.
    - - Therapeutic cloning involves the replication of human embryos to harvest stem cells for medical uses. Most clones are created through a process called "somatic cell nuclear transfer." Essentially, a scientist uses a tiny needle to pull DNA material from the nucleus of a donor cell and transfer it into a hollow egg
    - - During mitosis, the chromosomes, which have already duplicated, condense and attach to spindle fibers that pull one copy of each chromosome to opposite sides of the cell. The result is two genetically identical daughter nuclei.
      - Mitosis occurs wherever more cells are needed
    - - Advantages:
        It provides great potential for discovering treatments and cures to a variety of diseases including Parkinson's disease, schizophrenia, Alzheimer's disease, cancer, spinal cord injuries, diabetes and many more.
        Limbs and organs could be grown in a lab from stem cells and then used in transplants or to help treat illnesses.
        It will help scientists to learn about human growth and cell development.
        Scientists and doctors will be able to test millions of potential drugs and medicine, without the use of animals or human testers.
      - Disadvantages: unknown long term effects. Not always is the solution. The body may reject them
  - - - Common features of exchange surfaces:
        thin - for a short diffusion distance
        large area - achieved by being long and thin, flat, or folded
        moist - so that substances can be dissolved for diffusion to happen
    - - Osmosis is the movement of water from a high water concentration to a low water concentration through a partially permeable membrane. Osmosis takes place in all living cells.
        Plants absorb water from the soil by osmosis through their root hair cells. Plants use water for several vital processes including photosynthesis and transporting minerals.
    - - Larger organisms have a smaller surface area to volume ratio. small organisms can pass nutrients and other substances quickly through the membrane
    - - The rate of diffusion is increased when:
        The distance is decreased
        The surface area is increased
        The concentration difference (concentration gradient) is increased
    - - Active transport is the process by which dissolved molecules move across a cell membrane from a lower to a higher concentration. In active transport, particles move against the concentration gradient - and therefore require an input of energy from the cell.
    - - Diffusion occurs when particles spread. They move from a region where they are in high concentration to a region where they are in low concentration. Diffusion happens when the particles are free to move. This is true in gases and for particles dissolved in solutions.
    - - Active transport vs diffusion and osmosis
        Diffusion -Osmosis -Active transport
        Down a concentration gradient: ✓ ✓ ✗
        Against a concentration gradient: ✗ ✗ ✓
        Energy needed: ✗ ✗ ✓
        Substance moved: -Dissolved solutes -Water -Dissolved solutes
  - - - Cells may be specialised for a particular function. Their structure will allow them to carry this function out. Here are some examples:
        
        Root hair cell
        Absorbs water and mineral ions from the soil Long 'finger-like' process with very thin wall, which gives a large surface area.
        
        Sperm cell
        Fertilises an egg cell - female gamete The head contains genetic information and an enzyme to help penetrate the egg cell membrane. The middle section is packed with mitochondria for energy. The tail moves the sperm to the egg.
        
        Leaf cell
        Absorbs light energy for photosynthesis Packed with chloroplasts. Regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight.
        
        Red blood cells
        Contain haemoglobin to carry oxygen to the cells. Thin outer membrane to let oxygen diffuse through easily. Shape increases the surface area to allow more oxygen to be absorbed efficiently. No nucleus, so the whole cell is full of haemoglobin.
    - - Function of cells which animal and plant cells have in common
        nucleus- contains genetic material, which controls the activities of the cell
        cytoplasm- most chemical processes take place here, controlled by enzymes
        cell membrane- controls the movement of substances into and out of the cell
        mitochondria- most energy is released by respiration here
        ribosomes- protein synthesis happens here
        Plant cells also have extra parts:
        cell wall- strengthens the cell
        chloroplasts- contain chlorophyll, which absorbs light energy for photosynthesis
        permanent vacuole- filled with cell sap to help keep the cell turgid
    - - Differentiation is the process of cells becoming specialised. Most types of animal cells differentiate at an early stage.
      - Most plant cells can differentiate into different cell types Only stem cells can differentiate into different cell types. Other animal cell functions remain fixed.
    - - Magnification is the ability to make small objects seem larger, such as making a microscopic organism visible. Resolution is the ability to distinguish two objects from each other. Light microscopy has limits to both its resolution and its magnification.
    - - Light microscopes use light and mirrors to see up to 400 nanometers
        Electron magnifies can magnify up to 10 million times
    - - Bacteria are prokaryotes. They do not have a membrane-bound nucleus and their DNA is free in the cytoplasm.
      - Animals, plants and fungi are eukaryotes. They have a membrane-bound nucleus and their chromosomes are linear rather than circular.
- - - - Transmission - through rain
      - Treatment - spray with fungicide
      - Signs - Large black or dark purple spots on the surface of the leaves or stems are the main signs of black spot. As the problem gets worse the foliage gradually turns yellow and drops prematurely, weakening the plant.
    - - Salmonella infection usually occurs when a person eats food contaminated with the feces of animals or humans carrying the bacteria. Salmonella outbreaks are commonly associated with eggs, meat and poultry, but these bacteria can also contaminate other foods such as fruits and vegetables.
      - Neisseria gonorrhoeae cultured on two different media types. Neisseria gonorrhoeae, also known as gonococci (plural), or gonococcus (singular), is a species of Gram-negative coffee bean-shaped diplococci bacteria responsible for the sexually transmitted infection gonorrhea.
    - - HIV
        
        HIV (human immunodeficiency virus) is a virus that attacks the immune system, the body's natural defense system. Without a strong immune system, the body has trouble fighting off disease. Both the virus and the infection it causes are called HIV.
      - Tobacco mosaic virus (TMV) is a positive-sense single stranded RNA virus that infects a wide range of plants, especially tobacco and other members of the family Solanaceae. The infection causes characteristic patterns, such as "mosaic"-like mottling and discoloration on the leaves (hence the name).
      - Measles
        
        Measles is a highly contagious infection caused by the measles virus. Initial signs and symptoms typically include fever, often greater than 40 °C (104.0 °F), cough, runny nose, and inflamed eyes. ... Measles is an airborne disease which spreads easily through the coughs and sneezes of those infected.
      - Some of the diseases that are caused by viral pathogens include smallpox, influenza, mumps, measles, chickenpox, ebola, and rubella.
    - - Vaccination causes the body to produce enough white blood cells to protect itself against a pathogen. Antibiotics are effective against bacteria, but not against viruses. Some strains of bacteria are resistant to antibiotics.
      - Hygiene- wash hands
    - - Pathogens are microorganisms - such as bacteria and viruses - that cause disease. Bacteria release toxins, and viruses damage our cells. White blood cells can ingest and destroy pathogens. They can produce antibodies to destroy pathogens, and antitoxins to neutralise toxins.
      - Spread
        
        Contact
        
        Kissing
        
        Sexual intercourse
        
        Touching
        
        vehicle borne transmission
        
        water
        
        sharp objects
        
        Droplets in the air
        
        food