Cell structure and transport

• Cells are the basic unit of all forms of life. They can be eukaryotic
• Eukaryotic cells


  Have a nucleus (e.g. animal and plant cells)
• Parts of a plant cell

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Cell wall
  • Vacuole
  • Ribosome
• Nucleus


  Controls all cell activity and contains the DNA
• Cytoplasm


  A liquid gel where chemical reactions take place
• Cell membrane


  Controls the movement of substances in and out of the cell
• Mitochondria


  The site of respiration. Releases energy for the cell to use
• Ribosomes


  Where protein synthesis takes place. They make proteins
• Cell wall


  Strengthens the cell. In plant and algal cells it is made of a strong substance called cellulose
• Chloroplasts


  Where photosynthesis takes place. They can trap the light energy using a green pigment called chlorophyll
• Vacuole


  It is filled with cell sap and helps to keep the cell turgid and to support the plant
• Prokaryotic cells are smaller and do not have a nucleus. Their genetic material (DNA) is free and forms a single loop. All bacteria are prokaryotes
• Parts of a bacterial cell


  • Cell wall
  • Cytoplasm
  • Plasmid
  • Ribosome
• Cell wall


  For protection and to stop the bacterial cell from bursting
• Plasmid


  Small rings of extra bacterial DNA
• Ribosome


  Where proteins are made
• Light microscopes work by shining light through a specimen
• The light is then refracted through an objective lens and an eyepiece lens to form a magnified image on your eye
• Total magnification


  Objective lens magnification x Eyepiece lens magnification
• Magnification is how many times bigger the image is than the actual object you're looking at
• Resolution


  The ability to distinguish between two separate points. The greater the resolution, the finer the detail that you are able to see
• Electron microscopes use a beam of electrons instead of a beam of light, providing much greater resolution and magnification than light microscopes
• Diffusion is the net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient
• Factors affecting rate of diffusion

  • Temperature (higher temperature increases rate)
  • Surface area (larger surface area increases rate)
  • Concentration gradient (larger gradient increases rate)
• Osmosis


  The diffusion of water molecules from a dilute solution to a concentrated solution across a partially permeable membrane
• Adaptations for efficient diffusion in large multicellular organisms


  • Large surface area
  • Thin membrane
  • Efficient blood supply
  • Well ventilated
• Active transport


  Moves substances from an area of low concentration to an area of high concentration against a concentration gradient, requiring energy from respiration
• Active transport allows mineral ions to be absorbed into plant root hairs and glucose to be absorbed from the gut into the blood
• Active transport is achieved by special protein pumps in the cell membrane
• Cells begin to differentiate from an early stage in an organism's development, acquiring new internal structures to carry out specific functions
• Examples of specialised cells


  • Nerve cell (neurone)
  • Sperm cell
  • Muscle cell
  • Sieve plate cell
  • Phloem tube cell
  • Xylem vessel cell
  • Guard cell
  • Root hair cell
• Neurone


  Has dendrites and an axon to make connections and communicate with other cells
• Sperm cell


  Has an acrosome to release enzymes to penetrate the egg cell, and a haploid (half) nucleus
• Muscle cell


  Contains many mitochondria to release energy for contraction
• Sieve plate cell

  Has holes to allow the movement of dissolved sugars to be transported around the plant
• Phloem tube cell


  Lacks many internal structures, but has companion cells to help keep it functioning
• Xylem vessel cell


  Forms a hollow tube with thick, woody walls to transport water and mineral ions up the plant
• Guard cell


  Pairs of cells that can contract to open and close stomata
• Root hair cell


  Has a long extension of the cell membrane to increase the surface area for absorbing water and mineral ions from the soil
• How to prepare a stained slide of plant cells


  1. Put a drop of water on a slide

  2. Peel off a thin layer of tissue from an onion

  3. Place the onion tissue on the slide

  4. Add a drop of iodine stain

  5. Lower a coverslip carefully