Biology

• Eukaryotic cells


  Plant and animal cells that have a cell membrane, cytoplasm and genetic material enclosed in a nucleus
• Prokaryotic cells

  Bacterial cells that are much smaller, have cytoplasm and a cell membrane surrounded by a cell wall, and genetic material not enclosed in a nucleus
• Parts of animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional parts of plant cells

  • Chloroplasts
  • Permanent vacuole filled with cell sap
  • Cell wall made of cellulose
• Nerve cell


  • Carry electrical impulses around the body of an animal for rapid communication
  • Have long axons to carry information
  • Synapses are adapted to pass impulse to another cell
  • Lots of dendrites to make connections with other cells
  • Contain lots of mitochondria to provide energy that is needed to make neurotransmitters
• Sperm cell


  • Contain the genetic information of the male parent and move to reach an egg
  • Has an acrosome that contains enzymes for breaking through the egg
  • Middle section has lots of mitochondria to transfer energy needed for the tail to work
  • A long tail that moves from side to side to help the cell move
  • A large nucleus that contains genetic information
  • Streamlined shape
• Muscle cell


  • Cells that contract and relax to bring about movement
  • Store glycogen that can be used in respiration
  • Contain lots of mitochondria to transfer energy needed for cells to contract and relax
  • Contain proteins that slide over each other
• Palisade cell


  • A photosynthetic cell that carries out photosynthesis
  • Have a permanent vacuole to keep the cells rigid to keep the leaf spread out and the stem supported
  • Contain chloroplasts containing chlorophyll that absorb light for photosynthesis
  • Found in layers in the leaf and outer layers of the stem to absorb as much light as possible
  • Regular shape so that cells can be closely packed together
• Root hair cell


  • Take up water and mineral ions from the soil
  • Have lots of mitochondria to transfer energy for active transport of mineral ions
  • Have a large permanent vacuole to speed up the movement of water by osmosis
  • Have a large surface area for water to enter the cell
• Phloem cell


  • Cells that make up a tissue to transport food around the plant
  • The cell walls between the cells break down to form sieve plates
  • Have very few supporting structures
  • Supported by companion cells
  • The mitochondria of these cells provide energy to the other cell
• Xylem cell


  • Cells that make up a tissue to transport water around the plant
  • Have spirals and rings of lignin to make them very strong
  • The cells die and form long hollow tubes
• Cell parts and their functions

  • 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
  • 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
• Plant and animal cells (eukaryotic cells) have a cell membrane, cytoplasm and genetic material enclosed in a nucleus. Most animal cells have the following parts: nucleus, cytoplasm, a cell membrane, mitochondria, ribosomes. In addition to the parts found in animal cells, plant cells often have: chloroplasts, a permanent vacuole filled with cell sap. Plant and algal cells also have a cell wall made of cellulose, which strengthens the cell.
• Electron microscope


  Has much higher magnification and resolution than a light microscope, enabling the study of cells in much finer detail
• Electron microscopes are more expensive and take up more space, while light microscopes are easy to use and cheap
• Diffusion


  The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
• Substances transported by diffusion

  • Oxygen
  • Carbon dioxide
  • Urea
• Factors affecting rate of diffusion

  • Difference in concentrations (concentration gradient)
  • Temperature
  • Surface area of the membrane
• Osmosis


  The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Surface area to volume ratio

  A single-celled organism has a relatively large surface area to volume ratio, allowing sufficient transport of molecules into and out of the cell
• In multicellular organisms, surfaces and organ systems are specialised for exchanging materials to allow sufficient molecules to be transported into and out of cells for the organism's needs</b>
• Factors that increase the effectiveness of an exchange surface

  • Having a large surface area
  • A membrane that is thin, to provide a short diffusion path
  • Having an efficient blood supply
  • (in animals, for gaseous exchange) being ventilated
• Active transport


  Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient), requiring energy from respiration
• Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil, and sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration
• Adaptations of the small intestine

  • Sugar is absorbed by diffusion in the first part and by active transport in the later parts
  • Long
  • Villi
  • Thin membrane
  • Good blood supply
  • Lots of mitochondria
• Adaptations of root hair cells

  • Elongated shape
  • Lots of root hair cells
  • Thin membrane
  • Water/minerals removed quickly
  • Lots of mitochondria
• Adaptations of lungs and gills

  • Lots of alveoli (lungs), lamellae (gills)
  • Thin membrane
  • Good blood supply
  • Good ventilation
• Meristem


  Tissue in plants that can differentiate into any type of plant cell, throughout the life of the plant
• Uses of meristems


  • Rare species can be cloned to protect from extinction
  • Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers
  • Cloning allows growers to mass produce plants that may be difficult to grow from seed
  • All the plants are genetically identical, which is useful because you can be sure of their characteristics
• Stem cell


  An undifferentiated cell which is able to make many more cells of the same type through division and differentiation
• Types of stem cells

  • Adult stem cells
  • Embryonic stem cells
  • Meristems
• The cell cycle


  1. Stage 1: Cell growth and DNA replication

  2. Stage 2: Mitosis - One set of chromosomes is pulled to each end of the cell and the nucleus divides

  3. Stage 3: Cytoplasm and cell membranes divide to form two identical cells
• Uses of stem cells

  • Offer the possibility of a renewable source of replacement cells and tissues to treat diseases including macular degeneration, paralysis, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis, and rheumatoid arthritis
• Adult stem cells


  • Found throughout animals after development, multiply by mitosis to replenish dying cells and regenerate damaged tissue, can be found in bone marrow and form many types of cells including blood cells
• Therapeutic cloning


  An embryo is produced with the same genes as the patient, so stem cells from the embryo are not rejected by the patient's body and may be used for medical treatment
• Principles of organisation


  Cells are the basic building blocks of all living organisms, tissues are groups of cells with similar structure and function, organs are aggregations of tissues performing specific functions, organ systems are groups of organs that work together to form organisms
• Organs in the digestive system

  • Pancreas - Produces hormones to control blood sugar and enzymes that break down food
• The digestive system


  An organ system in which several organs work together to digest and absorb food, breaking down large insoluble molecules into smaller, soluble molecules that can be absorbed and used by cells
• Small intestine


  • Where the soluble food molecules are absorbed into the blood stream, adapted to have a very large surface area as it is covered in villi, has a good blood supply and short diffusion distances to blood vessels
• The stomach is an organ made up of muscular tissue, glandular tissue and epithelial tissue