Cell Structure and Transport

- light microscopes magnify up to about x2,000 and have a resolving power of about 200nm

- electron microscopes magnify up to about x2,000,000 and have a resolving power of around 0.2nm

    magnification = size of image / size of real object

- animal cell features common to all cells:

    a nucleus

    cytoplasm

    cell membrane

    mitochondria

    ribosomes

- plant and algal cells contain all the structures seen in animal cells as well as a cellulose cell wall

- many plants also contain chloroplasts and a permanent vacuole filled with sap

- eukaryotic cells all have a cell membrane, cytoplasm and genetic material enclosed in a nucleus

- prokaryotic cells consist of cytoplasm and a cell membrane surrounded by a cell wall, the genetic material is not in a distinct nucleus, it forms a single DNA loop,

    they may contain one or more extra small rings of DNA called plasmids

- bacteria are all prokaryotic

- as an organism develops, cells differentiate to form different types of cells

- as an animal cell differentiates to form a specialised cell it acquires different sub-cellular structures to enable it to carry out a certain function

- examples of a specialised animal cells are:

    nerve cells

    mucle cells

    sperm cells

- animal cells may be specialised to function within a tissue, an organ, organ systems or whole organisms 

-plant cells may be specialised to carry out a particular function

- examples of specialised plant cells are:

    root hair cells

    photosynthetic cells

    xylem cells

    phloem cells

- plant cells may be specialised to function within tissues, organs, organ systems or whole oganisms

- diffusion is the spreading out of particles of any substance, in solution or a gas, resulting in a net movement from an area of lower concentration, down a concentration, down a concentration gradient

- the rate of diffusion is affected by:

    the difference in concentrations

    the temperature

    the available surface area

- dissolved substances such as glucose and urea and gases such as oxygen and carbon dioxide move in and out of cells by diffusion

- osmosis is a special case of diffusion, it the movement of water from a dilute to a more concentrated solute solution through a partially permeable membrane that allows water to pass through

- differences in the concentrations of solutions inside and outside a cell cause water to move into or out of the cell by osmosis

- animal cells can be damaged if the concentration outside the cell changes dramatically

- osmosis is important to maintain turgor in plant cells 

- there are a variety of practical investigations that can be used to show the effect of osmosis on plant tissues

- scientists have discoverd ways of measuring the turgor pressure inside individual cells using tiny probes

- the pressure inside the root or leaf cell of a plant are far higher than human blood pressure, or even the pressure in a car tyre

- active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient)

- uses energy released from food in respiration to provide the energy required

- active transport allows plant root hairs to absorb mineral ions required for healthy growth from very dilute solutions in the soil against a concentration gradient

- enables sugar molecules used for cell respiration to be absorbed from lower concentrations in the gut into the blood where the concentration of sugar is higher

- single-celled organisms have a relatively large surface area to volume ratio so all necessary exchanges with the environment take place over this surface

- in multicellular organisms, many organs are specialised with effective exchange surfaces

- exchange surfaces usually have a large surface area and thin walls, which give short diffusion distances

- in animals, exchange surfaces will have an efficient blood supply or, for gaseous exchange, be ventilated