B1

Light Microscopes:

• Use a beam of light to form an image
• Can magnify objects up to 2000 times (but school microscopes usually up to 400 times)
• Can be used to view living objects
• Are relatively cheap 
• Easy to carry around

Electron Microscopes:

• Use a beam of electrons to form an image
• Can magnify objects up to 2,000,000 times
• Cannot be used to view living objects
• Very expensive
• Need to be kept in special conditions

Magnification=Image size/Object size

Animal cells contain structures such as:

• Nucleus
• Cytoplasm
• Cell Membrane
• Mitochondria
• Ribosomes

Plant cells contain structures such as:

• Nucleus
• Cytoplasm
• Cell Membrane
• Mitochondria
• Ribosomes
• Cell Wall
• Chloroplasts
• Permanent Vacuole

Nucleus: Controls the cells activity

Cytoplasm: A liquid gel in which the organelles are suspended, and where many chemical reactions take place

Cell Membrane: Controls the movement of substances such as glucose and mineral ions into the cell, and other substances such as urea and hormones out of the cell

Mitochondria: Where energy is transferred during aerobic respiration

Ribosomes: Where protein synthesis takes place

Cell Wall: Made of cellulose for support

Chloroplasts: Contain chlorophyll for photosynthesis; the chloroplasts absorb light to make food for the plant

Permanent Vacuole: Contains cell sap, which keeps the cell rigid and helps support the plant

All animals (including human beings), plants, fungi and protista are eukaryotes.

Eukaryotic cells contain a cell membrane, cytoplasm, and a nucleus. The nucleus contains chromosomes, which are made of the genetic material called DNA.

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

Examination of plant and animal cells using a light microscope and production of labelled scientific drawing from observation

Aims of the experiment:

• To stain cells for examination with a light microscope
• To examine a range of cells and other structures with a microscope to understand their basic sturctures.

Method:

• Put a small drop of water on the microscope slide.
• Peel some onion skin from inside of an onion leaf in an onion bulb
• Transfer to the drop of water. Stain the cell with iodine and observe through the microscope.

• Bacteria are very small and can only be seen with a powerful microscope.
• Bacteria cells have a cell membrane and a cell wall surrounding the cytoplasm.
• The cell wall is different from a plant cell wall because it is not made of cellulose.
• Bacteria do not contain a nucleus.
• The genetic material is found in the cytoplasm as a long circle of DNA called plasmids.

Nerve cells are specialised to carry electrical impulses to carry electrical impulses around the bodies of animals.

Nerve cells have:

• many dendrites to make connections to other nerve cells
• an axon to carry the impulse from one place to another
• nerve endings or synapses, which pass impulses to other cells by producing transmitter chemicals
• many mitochondria in the synapses to transfer the energy needed to make the transmitter chemicals.

Muscle cells contract and relax. Striated (striped) muscle cells are found in the muscles that enable your body to move. Smooth muscle cells are found in the tissues of the digestive system and contract to move food along the gut.

So muscle cells can contract they contain:

• special proteins that slide over each other
• many mitochondria to transfer the energy needed for chemical reactions
• a store of glycogen that can be broken down and used in respiration to transfer energy.

Sperm cells carry the genetic information from the male parent. They are specialised to move through water or the female reproductive system to reach the egg.

Sperm cells have:

• a long tail that whips from side to side to move the sperm
• a middle section full of mitochondria to transfer the energy needed by the tail to move
• an acrosome to store digestive enzymes to break down the outer layers of the egg

Root hair cells occur near the tips of roots. They increase the surface are of the root so that it can absorb water and mineral ions efficiently. Root hair cells are close to xylem tissue that transports water and mineral ions through the plant.

Root hair cells:

• increase the surface area available for water to move into the cell
• have a large permanent vacuole - speeds up the movement of water by osmosis from the soil across the root hair cell.

Plants can make their own food by photosynthesis.

Photosynthetic cells:

• have chloroplasts containing chlorophyll to trap the light needed for photosynthesis
• are often found in continuous layers in the leaf and outer layers of stems
• have a large permanent vacuole that helps to keep the cell rigid.

Xylem tissue has two main functions:

1. the xylem cells transport water and mineral ions from the roots to the stem and leaves.

2. Xylem tissue supports the plant.

• Xylem cells are living when they are first formed
• then a chemical called lignin builds up in spirals in the cell walls
• the cells die leaving hollow tubes.
• water and mineral ions can move up the tubes, the spirals of lignin make the xylem strong.

Phloem is the tissue that transports food made by photosynthesis to the rest of the plant. Phloem cells form tubes but do not become lignified like the xylem.

• The cell walls between phloem cells break down to form sieve plates,
• phloem cells lose a lot of their structures but are kept alive by companion cells which contain mitochondria that transfer energy to aid the movement of dissolved food in the phloem

Diffusion is the spreading out of particles of any substance, in solution or gas, resulting in a net movement from an area of high concentration to and area of low concentration down a concentration gradient.

The rate of diffusion is affected by the difference in concentrations, the temperature, and the available surface area.

In the lungs, the blood will continue to take in oxygen from the alveolar air spaces provided the concentration of oxygen there is greater than in the blood. Oxygen diffuses across the alveolar walls into the blood, and the circulation takes the oxygen-rich blood away.

Osmosis is a special case of diffusion. It is the movement of water from a dilute to a more concentrated solution through a partially permeable membrane that allows water to pass through.

Water can move across cell membranes because of osmosis. For osmosis to happen you need:

• two solutions with different concentrations
• a partially permeable membrane to separate them

Partially permeable membranes let some substances pass through them, but not others.

Active transport is the movement of molecules across a membrane from a region of their lower concentration to a region of their higher concentration - in the direction against the concentration gradient.

Active transport requires energy from respiration.

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.

Materials such as oxygen and soluble food molecules need to reach all cells, and metabolic waste materials must be removed efficiently.

• Small organisms have large surface area to volume ratio. Single-celled organisms are tiny and can gain enough of materials such as oxygen by diffusion through their surface.
• As organisms increase in size, their surface area to volume ratio decreases.
• Large, complex, organisms have many cells that are not in contact with the environment; so they have special exchance surfaces to obtain all the food and oxygen they need.
• Efficient exchange surfaces have a large surface area, thin membranes or a short diffusion path, and an efficient transport system - the blood supply in animals.
• Gaseous exchange surfaces in animals must be ventilated. Oxygen is absorbed by the alveoli in the lungs when air is drawn in during breathing. The alveoli have a large surface area and a good blood supply to carry the oxygen away and maintain a concentration gradient.
• The villi of the small intestine have a large surface area, a short diffusion path, and a good blood supply to absorb soluble food molecules.