biology

• eukaryotes are complex cells made up of a nucleus and other membrane-bound organelles. They are found in multicellular organisms such as animals, plants, and fungi.

  Prokaryotic cells are simple cells that lack a nucleus and other membrane-bound organelles.
• light microscopes use light and lenses to form an image of the specimen.

  electron microscopes use electrons instead of light and have a higher magnification and resolution (sharper image).
• to prepare a slide:

  1. add a drop of water to a clean slide.
  2. place what you are magnifying onto the slide with some water.
  3. add iodine solution. this is a stain to highlight objects in a cell.
  4. place a cover slip on top and try not to get air bubbles in.
• image size = actual x magnification
• a specialised cell is a cell that performs a specific function.

  cells that are undifferentiated are stem cells.
• specialised cells include:

  1. sperm cellsnerve cells

  muscle cells

  root hair cells
• the nucleus contains chromosomes.

  chromosomes are long lengths of DNA.

  genes control characteristics.
• mitosis is when a cell reproduces itself by splitting to form two identical offspring.

  mitosis is used to grow and develop or replace cells.
• cell cycle

  1. DNA is spread out into long strings.
  2. cell duplicates its DNA. then mitosis occurs.
  3. the chromosomes line up at the centre of the ell and cell fibres pull them apart.
  4. membranes form around each of the sets of chromosomes. these become the nuclei of the two cells.
  5. the cytoplasm and cell membrane divide.
• explain how many cells would be present in a human embryo after 3 cell divisions using mitosis

  8
• binary fission is done by prokaryotes to divide.
• process of binary fission

  1. circular DNA and plasmids replicate.
  2. cell gets bigger and DNA strands move to opposite ends of the cell.
  3. cytoplasm begins to divide and new cell walls begin to form.
  4. cytoplasm divides and two daughter cells are produced.
• bacteria need a warm environment and lots of nutrients to divide quickly.
• to prepare an uncontaminated culture:

  • Petri dish and agar sterilised before use

  • to kill unwanted bacteria

  • inoculating loop passed through flame / sterile swab• to sterilise / kill (other) bacteriaInoculation

  • loop/swab used to spread/streak bacterium onto agar• lid of Petri dish opened as little as possible

  • to prevent microbes from air entering

  Post-inoculation

  • sealed with tape

  • to prevent microbes from air entering• incubate

  • to prevent microbes from air entering
• the digestive system is an organ system that breaks down food in humans.
• blood enters the heart through the pulmonary vein.
• • Arteries carry blood away from the heart straight after it has been pumped. This means it is under high pressure. The walls of arteries are made of thick muscle to withstand this pressure. This muscle is also elastic to allow a pulse of blood to travel along when your heart beats.
• • Veins carry blood back to the heart. This blood is under lower pressure because some of it has been lost as it travelled around your body. The walls of veins are made of thinner muscle and are less elastic than arteries. Because the blood is under lower pressure, one-way valves in your veins stop it flowing backwards.
• • Capillaries are the tiny blood vessels that branch out into every tissue in your body carrying substances your cells need like oxygen and glucose for respiration and for removing waste products like carbon dioxide. They have very thin walls to allow these substances to move by diffusion in and out of your cells. Capillaries join your arteries to your veins. they are one cell thick
• The two top chambers in the heart are called atria (right atrium and left atrium) and the bottom chambers are called ventricles (right ventricle and left ventricle).

  The atria collect blood and then pump them to the ventricles below. The ventricles then pump the blood to the body. It looks as though the ventricles are bigger but the four chambers inside are the same size. It is the muscular lining of the ventricles that are bigger because they have to pump the blood further than the atria to the rest of the body.
• Benign tumours grow slowly and within a membrane, so they cannot spread. Malignant tumours grow quickly and can spread to affect other organs (metastasis).
• Root hair cells: specialised to

  1. take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots
  2. Have a large surface area due to root hairs, meaning more water can move in
  3. The large permanent vacuole affects the speed of movement of water from the soil to the cell
  4. Mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell
• Xylem cells:

  1. specialised to transport water and mineral ions up the plant from the roots to the shoots
  2. Upon formation, a chemical called lignin is deposited which causes the cells to die. They become hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through
  3. Lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water
• Phloem cells:

  1. specialised to carry the products of photosynthesis (food) to all parts of the plants
  2. Cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell
  3. Despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cells.
• Surface area of the membrane

  • As the surface area of the membrane increases, the rate of diffusion also increases, as there is more space for molecules to diffuse across the membrane
• Temperature

  As the temperature increases, particles gain more kinetic energy and so can diffuse across a membrane more quickly. Therefore, as the temperature increases, the rate of diffusion increases
• Difference in concentration

  The greater the concentration gradient, the quicker diffusion takes place
• Difference in concentration

  • If there is a very high concentration of oxygen in the alveoli, and a very low concentration in the blood, diffusion will take place very quickly. However, if there is an almost equal concentration in both, the rate of diffusion will be very low
• Membrane

  • Thin
  • Shorter diffusion pathway
• Adaptations for gas exchange

  • All gas exchange surfaces have features to increase the efficiency of gas exchange including:
  • Large surface area to allow faster diffusion of gases across the surface
  • Thin walls to ensure diffusion distances remain short
  • Good ventilation with air so that diffusion gradients can be maintained
  • Good blood supply (dense capillary network) to maintain a high concentration gradient so diffusion occurs faster
• Amylase

  An enzyme produced in the salivary glands and pancreas that breaks carbohydrates down into simple sugars
• Aorta

  The main artery that takes oxygenated blood away from the heart to the body
• Artery

  A blood vessel that carries blood at high pressure away from the heart
• Benign tumour

  An abnormal cell growth that is contained within one area and does not invade other areas of the body
• Bile

  A substance made in the liver and stored in the gallbladder which is used to neutralise stomach acid in the intestine and emulsify fats
• Blood

  A tissue containing red blood cells, white blood cells, platelets and plasma
• Cancer

  A non-communicable disease caused by changes in the cell that lead to uncontrolled growth and division
• Capillary

  A very thin blood vessel that is used for exchange of substances
• Cell

  The basic building block of all living organisms
• Communicable disease

  A disease that can be spread between individuals either directly or indirectly