Cell Biology

What is the difference between eukaryotic and prokaryotic cells?

Eukaryotic - DNA enclosed in nucleus. Prokaryotic - much smaller, no nucleus, single circular DNA loop + may contain plasmids.

What structures are found in animal cells and their functions?

Nucleus - genetic material/controls cell. Cytoplasm - chemical reactions. Cell membrane - controls movement in/out. Mitochondria - aerobic respiration. Ribosomes - protein synthesis.

What extra structures do plant cells have?

Cellulose cell wall - strengthens cell. Chloroplasts - photosynthesis. Permanent vacuole - contains cell sap.

What structures are found in bacterial cells?

Cell membrane, cytoplasm, cell wall, single circular DNA loop + possible plasmids. No nucleus.

What scale prefixes must you know?

centi = 10^-2, milli = 10^-3, micro = 10^-6, nano = 10^-9.

What are the key microscopy unit conversions?

1 mm = 1000 micrometres. 1 micrometre = 1000 nm.

What is an order of magnitude?

A difference of 10 times. E.g. 10^-5 m is one order of magnitude larger than 10^-6 m.

How can you estimate relative size or area from a cell image?

Compare how many times one structure could fit across or inside another.

How is a sperm cell specialised?

Tail - movement. Many mitochondria - energy. Acrosome - enzymes to penetrate egg.

How is a nerve cell specialised?

Long axon - impulses over long distances. Branched ends - connect to cells. Myelin - insulation/speeds impulses.

How is a muscle cell specialised?

Contractile fibres - contraction. Many mitochondria - energy for contraction.

How is a root hair cell specialised?

Long extension - large surface area. Many mitochondria - energy for active transport of mineral ions.

How is xylem specialised?

Dead, hollow cells joined end-to-end - water/mineral transport. Lignin - strengthens/supports.

How is phloem specialised?

Sieve tubes - transport dissolved sugars by translocation. Companion cells - provide energy.

What is cell differentiation?

Process by which a cell changes to become specialised for a particular function.

How does differentiation differ in animals and plants?

Animals - most cells differentiate early. Plants - many cells retain ability to differentiate throughout life.

What happens to cell division in mature animals?

Mainly restricted to repair and replacement.

What happens when a cell differentiates?

Develops different sub-cellular structures suited to its function.

What is the difference between magnification and resolution?

Magnification - how many times larger an image is. Resolution - ability to distinguish two close points separately.

Why can electron microscopes show more detail than light microscopes?

Much higher magnification + resolution - smaller sub-cellular structures can be seen.

What is the magnification equation?

Magnification = image size / real size.

How can you rearrange the magnification equation?

Image size = magnification x real size. Real size = image size / magnification.

RP1 - How do you prepare and observe cells using a light microscope?

Thin specimen - slide - stain - coverslip - start low power - focus - increase magnification - draw and label.

RP1 - Why is a stain used in microscopy?

Increases contrast - structures are easier to see.

RP1 - What makes a good biological drawing?

Clear single lines, no shading, correct proportions, labels + magnification scale.

How do bacteria reproduce?

Binary fission - one cell divides into two.

What conditions allow rapid bacterial growth?

Sufficient nutrients + suitable temperature.

How can microorganisms be cultured?

Nutrient broth or colonies on agar gel.

How do you calculate the number of bacterial divisions?

Number of divisions = total time / mean division time.

How do you calculate bacterial population after binary fission?

Final population = initial population x 2^number of divisions.

How should very large bacterial populations be written at Higher Tier?

Standard form - e.g. 3.2 x 10^8.

How do you calculate the area of a bacterial colony or inhibition zone?

Area = pi x radius^2.

Why must microbial cultures be uncontaminated?

So results are caused by the microorganism being investigated, not contamination.

How is an uncontaminated bacterial culture prepared?

Sterilise Petri dish/agar - flame inoculating loop - minimise lid opening - tape lid - incubate upside down at maximum 25°C.

Why sterilise Petri dishes, agar and inoculating loops?

Kills unwanted microorganisms - prevents contamination.

Why are cultures incubated at a maximum of 25°C in school?

Reduces growth of potentially harmful pathogens.

Why are agar plates stored upside down?

Prevents condensation dripping onto agar and spreading colonies.

RP2 - How do you investigate antibiotics or antiseptics?

Spread bacteria on sterile agar - add treated discs + control - incubate - measure zones of inhibition.

RP2 - What does a larger zone of inhibition mean?

Greater inhibition of bacterial growth - more effective antibiotic/antiseptic.

RP2 - Why use a control disc?

Shows inhibition is caused by antibiotic/antiseptic, not the disc or solvent.

What is the relationship between chromosomes, DNA and genes?

Chromosomes are made of DNA. Each chromosome carries many genes. Body-cell chromosomes are normally in pairs.

What are the three overall stages of the cell cycle?

1 - growth + DNA replication. 2 - mitosis. 3 - cytoplasm and cell membrane divide.

What happens before mitosis?

Cell grows - increases sub-cellular structures - DNA replicates to form two copies of each chromosome.

What happens during mitosis?

One set of chromosomes pulled to each end - nucleus divides.

What happens after mitosis?

Cytoplasm + cell membrane divide - two genetically identical cells form.

Why is mitosis important?

Growth, development, repair + replacement.

What is a stem cell?

Undifferentiated cell that can divide and differentiate into specialised cells.

Compare embryonic, adult and plant stem cells.

Embryonic - most human cell types. Adult bone marrow - several types including blood cells. Meristem - any plant cell throughout life.

How could human stem cells treat disease?

Replace damaged/faulty cells - potential treatment for diabetes and paralysis.

What is therapeutic cloning?

Embryo has same genes as patient - stem cells are genetically matched so not rejected.

What are the benefits and risks of embryonic stem cells?

Benefits - can form most cell types and treat disease. Risks/issues - viral infection + ethical/religious objections.

How are plant meristem stem cells useful?

Produce clones quickly/cheaply - protect rare species + mass-produce crops with desirable features.

Define diffusion.

Net movement of particles from high to low concentration - down a concentration gradient.

Which substances commonly move by diffusion in humans?

Oxygen + carbon dioxide in gas exchange. Urea from cells into blood for excretion.

What increases the rate of diffusion?

Larger concentration gradient, higher temperature + larger membrane surface area.

Why can single-celled organisms rely on diffusion?

Large surface area to volume ratio - sufficient exchange across cell surface.

How do you calculate surface area to volume ratio?

Surface area / volume.

How does organism size affect surface area to volume ratio?

As size increases - SA:V decreases.

Why do large multicellular organisms need exchange surfaces and transport systems?

Small SA:V + longer diffusion distances - diffusion alone cannot meet cell demands.

What makes an exchange surface efficient?

Large surface area + thin membrane. Animals - good blood supply. Gas exchange - ventilation.

What specialised exchange surfaces must you know?

Small intestine - digested food. Lungs/gills - gases. Roots - water/minerals. Leaves - gases.

Define osmosis.

Diffusion of water from a dilute to concentrated solution through a partially permeable membrane.

What happens to plant cells in dilute and concentrated solutions?

Dilute - water enters - turgid. Concentrated - water leaves - flaccid/plasmolysed.

How do you calculate percentage change in mass?

Percentage change = (final mass - initial mass) / initial mass x 100.

How do you calculate rate of water uptake?

Rate = amount of water taken up / time.

RP3 - How do you investigate osmosis in plant tissue?

Equal plant pieces - initial mass - different solution concentrations - same time - blot dry - final mass - calculate percentage change.

RP3 - What variables should be controlled?

Plant type/size, solution volume, time + temperature.

RP3 - Why blot plant tissue before final mass?

Removes surface solution - mass change reflects osmosis only.

RP3 - What should you plot on an osmosis graph?

Solution concentration - x-axis. Percentage change in mass - y-axis.

RP3 - What does 0% change in mass mean?

No net movement of water - solution concentration approximately equals cell contents.

What graph skills can be tested with osmosis data?

Plot data, draw appropriate line/curve, interpret trends + estimate values from graph.

Define active transport.

Movement from low to high concentration - against concentration gradient - using energy from respiration.

Why do root hair cells use active transport?

Absorb mineral ions when concentration is lower in soil than inside root cells.

Why is active transport needed in the small intestine?

Absorbs sugars into blood even when concentration is lower in intestine than blood.

Compare diffusion, osmosis and active transport.

Diffusion - particles high to low, no energy. Osmosis - water dilute to concentrated through partially permeable membrane, no energy. Active transport - substances low to high, requires energy.