Intermediate Two Biology

Unit 1: Living Cells Summary Notesa) Cell Structure and Function

Animal CellsAnimal cells have a nucleus, cell membrane and cytoplasm

Plant cellsPlant cells have all animal cell parts plus a cell wall, vacuole and chloroplasts. The presence or absence of a cell wall tells you if it is a plant or animal cell.

Yeast cells

Yeast cells have nucleus, cell membrane, cytoplasm and cell wall. They have no chloroplasts (cannot make their own food). They reproduce by budding.

Functions of cell structures

Structure Function Found inNucleus Contains genetic material.

Controls cells activitiesAll cells (except red blood cells)

Cytoplasm

Nucleus

Cell membrane

Chloroplast

Nucleus

Cell wall

Vacuole

Cell membrane

Cytoplasm Cytoplasm

CytoplasmCell membrane

NucleusCell wall

Cell membrane

Controls movement of substances into and out of the cell

All cells

Cytoplasm Site of chemical reactions All cellsVacuole Contains cell sap (sugary water) PlantsChloroplast Site of photosynthesis Some plant cellsCell wall Gives cell support and shape Plant and yeast cells

Commercial and Industrial uses of cells

Bread Making Uses yeast cells Anaerobic respiration (no oxygen present) of yeast produces carbon

dioxide Carbon dioxide causes dough to rise

Alcohol Production Uses yeast cells Anaerobic respiration

(fermentation) of yeast on sugar produces alcohol (ethanol)

Used to produce beer and wine

Antibiotic Production Uses fungi Fungi produce a wide

range of antibiotics to kill bacteria

Some bacteria are sensitive- the antibiotics prevent growth and destroy bacterial cells

Some bacteria are resistant- the antibiotics do not work

Resistant bacteria are on the increase due to overuse of antibiotics

CO2

Yo

ghurt Production Uses bacteria Bacteria convert lactose sugar in milk into lactic acid Decrease in pH causes curdling (thickening) of milk

Souring of milkLactose Lactic acid

Alternative Fuel Production Biogas

oUses bacteriaoBacteria produce methane gas from anaerobic breakdown of waste

products e.g. sewage Gasohol

oUses yeastoFermentation of sugar cane produced alcohol which is mixed with

petrol

b) Diffusion and Osmosis in plant and animal cellsDiffusion

Movement of substances from a high concentration to a low concentration down a concentration gradient

Food (glucose, amino acids) and oxygen enter cells by diffusion Carbon dioxide and waste products (urea) leave cells by diffusion Important process to cells

o Gain raw materials for respiration and photosynthesiso Removal of waste products

Osmosis

Special case of diffusion involving water only Movement of water across a selectively permeable membrane from an area

of high water concentration to a low water concentration Osmosis causes the change in weight of cells in water solutions Isotonic solutions have the same water concentration as a cell. There is no

net movement of water Hypotonic solutions are weak solutions and have a high water concentration.

Water will move into a cell. Hypertonic solutions are strong solutions and have a low water

concentration. Water will move out of a cell.

Test tubes A and B are hypotonic solutions as potato gained mass from taking in water by osmosis

Test tubes C, D and E are hypertonic solutions as potato lost mass from losing water by osmosis

Test tube B is closest to an isotonic solution because the mass of the potato changed the least

Dissolved food

Oxygen Waste products

e.g. CO2

Test Tube Concentration of sugar (M)

Percentage change in mass of potato

A 0.1 +10B 0.2 +5C 0.3 -10D 0.4 -15E 0.5 -25

Osmotic Effects in Plant cells

Hypertonic solution Isotonic solution Hypotonic solution Water moved out

of cell Cell

plasmolysed Vacuole has

shrunk Cell membrane

came away from cell wall

Flaccid

Cell appears normal

Water has moved into cell

Turgid Vacuole has

increased in size Cytoplasm

pushed against cell wall

Cell wall stretched to a maximum

Osmotic effect in Animal Cells

Hypertonic solution Isotonic solution

Hypotonic solution

Water moved out of cell

Cell shrunk/shrivelled

Cell appears normal

Water has moved into cell Cell has burst as no cell wall to

hold shape

c) Enzyme ActionCatalysts Speed up chemical reactions Lower energy input required for chemical reactions Take part in reactions but remain unchanged and can be used again

Enzymes Biological catalysts Made by all living cells Required for functioning of living cells

Made of protein

Specificity of Enzymes Active site of enzyme is where the

chemical reaction takes place It is complementary to one substrate

(lock and key hypothesis) Enzymes can only react with one

substrate/ perform one reaction

Enzyme reactions Degradation

o Chemical breakdown of a substanceo E.g. catalase breaks down hydrogen peroxide into water and oxygeno E.g. amylase breaks down starch into maltose

Synthesiso Building of a complex molecule from simpler moleculeso E.g. phosphorylase builds up glucose-1-phosphate into starch

Factors affecting enzyme activity Optimum conditions

o Enzymes have a temperature and pH value it works best ato Produces high volume of product at a fast rateo Activity increases to an optimum value then decreaseso Optimum value is peak of enzyme activity graph

Temperatureo Enzymes are made of protein which changes shape at high

temperatures

o This changes the shape of the active site and the substrate can no longer react with the active site of its enzyme

o The enzyme is denatured at high temperatures

pH o Enzymes have a small range of pH values it can work in

d) Aerobic and Anaerobic respiration

Energy release Chemical

energy in a cell is

contained in glucose

Energy released through series of enzyme controlled reactions- respiration

Glucose + oxygen energy + carbon dioxide + water Some energy released as heat Most energy used for cellular activities

Role of ATP

Energy from breakdown of glucose used to make ATP from ADP + Pi ATP used as energy source Used to transfer energy

Aerobic pathway

Glycolysiso First stage of respirationo Does not require oxygeno Glucose split into 2 pyruvic acid moleculeso 2 ATP produced

Oxygen dependant stageso Only occurs if oxygen is presento Pyruvic acid is completely broken down to carbon dioxide and water o 36 ATP producedo Aerobic respiration produces 38 ATP in total

Anaerobic Pathway

Only Glycolysis occurs Animal cells

o Pyruvic acid converted to lactic acido Reversible in presence of oxygen

Repayment of oxygen debt

Anerboic respiration in plant cells

o Pyruvic acid converted to alcohol (ethanol) and carbon dioxideo Carbon dioxide is released into atmosphere

Irreversible

e) Photosynthesis Series of enzyme-controlled reactions Carbon dioxide + water glucose + oxygen

Energy fixation Sunlight source of energy Sunlight trapped by chlorophyll in chloroplasts Converted into chemical energy (ATP) ATP used to produce glucose

Photolysis

Requires light Breakdown of water to produce hydrogen, oxygen and ATP Oxygen is released as by product to atmosphere by diffusion

During time P Anaerobic

respiration Production of lactic

acid

During time Q Repayment of

oxygen debt Lactic acid

converted to pyruvic acid

Hydrogen and ATP is carried to next stage

Carbon fixation

Hydrogen from stage one is joined with carbon dioxide to produce glucose

Uses ATP from photolysis as energy source Glucose stored as

o starch in leaveso cellulose in cell walls

Limiting factors of photosynthesis

Light intensity Carbon dioxide concentration Temperature

Carbon

Limiting factor at point 1: carbon dioxide concentration o Compare rate of photosynthesis with the graph for the higher carbon

concentration, the only difference is the carbon dioxide concentration therefore it must be the limiting factor

Limiting factor at point 2: light intensityo As graph is increasing due to higher concentration of carbon dioxide, it

must be the light intensity which is limiting the rate of photosynthesis

Removing a limiting factor

Use of heaters Use of lamps Adding carbon dioxide

o Increases glucose productiono Plants grow fastero Allows plants to be harvested sooner

Carbon