Investigating Cells

Investigating Cells

Interactive Summaries

This is an interactive exercise were you can fill in the correct blanks as you go! The Investigating Cells unit is divided into 4 sub-units:

• Investigating Living Cells
• Investigating Diffusion
• Investigating Enzymes
• Investigating Cell Division

The first sets of summaries in each sub-unit are all at GENERAL LEVEL!

To select an answer for each blank simply click on the grey box and choose your answer. You can check your answer by using the F1 key.

Investigating Living Cells

What are cells?

• Cells are the basic units of all living plantsliving animalsliving things
• A unicellular organism is made up of one cell. For example a cheek cellbacteriumblood cell
• A multicellular organism is made up of many cells. For example a cactus plant.
• When a Biologist wants to observe cells they use a microscope. The Biologist will stain the cells to allow them to see the cellsstructurestissue more clearly.
• An example of a stain that could be used is starchiodinebenedict's solution

Structures of Animal and Plant Cells

• The diagram below shows an animal cell.

nucleuscell membranecytoplasm

nucleus

nucleuscell membranecytoplasm

• The diagram below shows a plantan animalcell.

• The structure coloured blue is the chloroplastvacuolecell wall , the structure coloured green is the vacuolechloroplastcell wall and the structure coloured red is the chloroplastcell wallvaculoe.

Structure and Functions of Cells

Summary of Animal and Plant Cells

Investigating Diffusion

What is Diffusion?

• The molecules of a liquid and a solidgasmove about freely all the time.

• Diffusion is the movement of a gasliquidsubstancefrom a region of lowhighequal concentration to a region of highequallow concentration until concentrations areequalgreaterless.

Diffusion in Cells

• Diffusion allows substances to enter and exit cells. Substances that would enter a cell by diffusion are starchsucroseglucose and carbon dioxideoxygenfat . Substances that would exit a cell by diffusion are oxygencarbon dioxidesucroseand waste.

• The nucleuscell membranectyoplasmcontrols the passage of substance into and out of cells.

• The cell membranenucleusvacuole is freely permeable to small substances. Large molecules such as glucosewaterstarch are unable to pass through.

Cell membrane

Osmosis

• Osmosis is the movement of water from a region of highlowequalwater concentration to a region of highlowequal water concentration across a fully permeableselectively permeablemembrane.

Investigating Enzymes

What is an Enzyme?

• A chemical that slows downstopsspeeds up a chemical reaction and yet remains itself unaltered is called asubstratecatalystreactor.

• Anenzymeis a biological catalyst and it is made ofcarbohydratefatprotein.

• Many different enzymes are made by and are present in allliving cellsanimal cellsplants cells.

• In the absence of enzymes, biological processes such as respiration would proceed at too quicktoo slowa rate to maintain life.

• Enzymes are required for the functioning of living cells because they stopincreasedecrease the rate of biochemical reactions to a level high enough to support life.

Breakdown Reactions

• A breakdown or degradation reaction involves the breakdown of large simplesmall complexlarge complexmolecules into smaller simplerlarger simplerlarger complexmolecules.

• A substance in which an enzyme acts on is called thesubstrateproduct.

• The substance(s) produced by a reaction is called the product.

• The table shows examples of breakdown reactions:

Build up Reactions

• A build up or synthesisdegradation reaction builds up simple molecules into large complex molecules.

• The reaction below is an example of a build up reaction:

lipasephosphorylasecatalase

Glucose – 1 – phosphate starch

The Effect of Temperature on Enzyme Activity

• Enzymes are fairly activeinactiveat low temperatures, but not destroyed.

• As temperature increases enzyme activity will gradually increase until an ideal temperature is reached.

• As temperture increases beyond this ideal temperature, enzyme activity will increasedecreasestay the same. This is because at temperatures at or above 50ºC enzymes are normally destroyed or denaturedkilleddissolved .

The Effect of Different pH Ranges on Enzyme Activity

• Each enzyme works best at a particular pH.

• The pH range will depend on the conditions in which it normally operates. For example lipaseamylasepepsin is suited to the acidic conditions of the stomach which are pH 9-1011-122-3.

• The working pH range of the enzyme catalse is pH 7-11. It is most active at around pH7pH 10pH 9. Catalse works welldoes not workworks slowlyoutside this pH range.

• Within an ideal pH range of an enzyme its activity will gradually increasedecreaseuntil it reaches its ideal pH. After this point the enzyme activity will increasedecrease.

Investigating Cell Division

What is cell division?

• Cell division is the means by an organism increasesdecreases its number of cells.

• In a unicellular organism cell division is a form of growthreproduction , making two new individuals.

• In a multicellular organism cell division results in growth of the original organism.

• respirationmitosisreproduction is the biological term for cell division.

• In this process the nucleus divides into two motherfatherdaughter nuceli each of which have exactly the same number of cellschromosomes as were present in the original nucleus.

• The following diagram below shows the six main stages of mitosis:

• Stage (a) & (b) The nucleus contianing uncoiled chromosomes each dividesplitrelicate to form two identical chromatids.

• Stage (c) The chromosomes become longerthinnershorter and more visible. cellnuclear membrane disappears.

• Stage (d) The chromosomes line up along the sidesequator of the cell. Spindle fibres form amd each choromsome becomes attached by its centromerechromatid.

• Stage (e) Pair of identical chromatids separate and move to opposite sidespolesequators of the cell.

• Shage (f) Seperated chromatids now called centromereschromosomeschiasmata. New Nuclear membrane will form. nucleusvacuolecytoplasm divides to form two identical daughtermotherfather cells containing the same number of chromosomes as the original cell.

This is the end of the General section. Well done!!

Take note of sections you found difficult and remember to ask your Biology teacher for help!

Now try the Credit section of Investigating Cells!