B1

Eukaryotic Cells

All plants, fungi, humans and protista

Contains: a cell membrane, cytoplasm and nucleus (contains chromosomes)

Prokaryotic Cells

Bacteria (single cell organisms)

Only seen with a powerful microscope (0.2- 2um)

Contains: cell membrane, cell wall (not made of cellulose), cytoplasm (genetic matrial found here as long circle of DNA- some have extra rings of DNA called plasmids)

Do NOT have a nucleus

Some have bacteria protective slime capsule & others have flagella for movement

May bacteria may cause food to decomppsoe

When bacteria multiply, they form a colony

If a cell is less than 10 times bigger than another cell, they have the same order of magnitude- they are similar sizes

If a cell is 10 times bigger than another cell, it is 10^1 bigger or one order of magnitude bigger

If a cell is 100 times bigger, it is 10^2 or two orders of magnitude bigger

REQUIRED PRACTCAL 1

You can use a light microscope to look at animal cells as well as onion cells and either Elodea or algal cells.

All plant cells have a cell wall, cytoplasm, and a vacuole

Elodea and algal cells have chloroplasts for photosynthesis, but onion cells do not

Root Hair Cells

Occur near the tips of the roots

Increase surface are a of the root so that it can absorb water and mineral ions efficiently

Close to xylem tissue

• greatly increase the surface area available for water to move into cell
• have a large permanent vacuole- speeds up the movement of water by osmosis form the soil across the root hair cell
• have many mitochondria- transfer energy needed for the active transport of mineral ions inot the root hair cells

Photosynthetic Cells

• Chloroplasts containing chlorophyll to trap lihgt needed
• Often found in continuous layers in the leaf and outer layers of the stem
• Have a large permannent vacuole which keeps the cell rigid

Xylem Cells

They have two main functions-

• transports water and mineral ions from roots to the stem and leaves
• xylem tissue supports the plant

• Living when they are firts formed
• Then a chemical called lignin builds up spirals in cell walls
• The cells die, leaving hollow tubes. Water and minerals move up the tubes
• The spirals and rings og lignin make the xylem tubes very strong

Phloem Cells

A tissue that transports food made by photoysnthesis to the rest of the plant

Form tumes but do ot 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
• The companion cells contain mitochondria that transfer energy to aid the movement of dissolved food in the phloem

The spreading out of gas particles, or any subtsance in a colution (a solute) (freely permeable)

• The net movement into or out of cells depends on the concentration of the particles on each side of the cell membrane
• High to low concentration (because the particles move randomly)
• The differene in concentration between two areas is called the concentration gradient
• The larger the difference in concentration, the faster the rate of diffusion

• the diffusion of oxygen and glucose inot the cells of the body from the bloodstream for respiration
• the diffusion of carbon dioxide into actively photosynthesising plant cells
• the diffusion of oxygen and carbon dioxide in opposite directions in the lungs (gas exchange)
• the diffusion of simple sugars and amino acids from the gut through cell membranes

The diffusion of water across a partally permeable membrane (only allows certain substances to pass through)

• Requires no energy from cell
• Moves from high water concentration (a dilute solution) to a region of lower water concentration (a more cncentrated solution)

Isotonic- if the two solutions have the san concentration

Hypertonic- the solution that is more concentrated (has less water & more solute)

Hypotonic- the solution is more dilute

Animal cells that are surrounded by a hypotonic solution will swell and possibly burst because water moves inot the cell by osmosis

If the solutuion around animal cells is hypertonic, then water moves out of the cells and they shrink

Animals need complex mechanisms to control the concentration of the solutions around their cells to avoid bursting or shrinking

Turgor pressure occurs when no more water can enter the cell due to pressure inside

Water moves into plants by osmosis...the vacuole swells...the cytoplasm is pressured against the cell wall...the cell becomes rigid...the leaves and stem become rigid...

• As long as the outside solution is HYPOTONIC, water moves IN and keeps the cells RIGID, which supports the plant
  
• Plant cells in a HYPERTONIC solution LOSE water and become FLACCID, so the plant WILTS
• When plant cells are placed in a HYPERTONIC solutions in the lab, a lot of water LEAVES THE CELL. the vaculoe and cytoplasm SHRINK, the the membrabes PULLS AWAY from the cell wall- PLASMOLYSIS

Plant tissue reacts so strongly to the concentration to the cncentration of the external solution that you can use an osmometer (a way of meauring osmosis)

Put plant tissue into different concentrations of salt or sugar solutions

If plant tissue is placed in a HYPOTONIC solution, water will move INTO the cell by osmosis

If plant tissue is placed in a HYPERTONIC solution, water will move OUT of the cell by osmosis

MEASURE CHANGE IN MASS

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

• Small organisms- 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- many cells that are not in contact with the environment, so they have special exchange surfaces to obtain all food and oxygen needed
• Efficient exchange surfaces- large surface area, thin membranes or short diffusion path, efficient transport system the blood supply in animals)
• Gaseous exchange surfaces in animals- must be ventilated, oxygen is absorbed by alveoli (large surface area and good blood supply to carry oxygen and maintain concentration gradient) in the lungs where air is drawn in during breathing
• The villi of small intestine- large surface area, short diffusion oath, good blood supply to absorb molecules of food

• Fish gills- gaseous exchnage surface between water and the blood. A flap, the operculum, acts as a pump to maintain the flow of water and the blood. The blood carries the oxygen away to maintain a concentration gradient
• Plants- long, thin roots to increase surface area for water absorption, root hair cells increase SA even more
• Plant leaves- flat and thin internal air spaces and stomata allow gases in and out of leaves