Biology EOY

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Parts of an animal cell

Nucleus (contains DNA, controls cell), cytoplasm (where reactions happen), cell membrane (controls what enters/exits), mitochondria (aerobic respiration), ribosomes (protein synthesis)

Extra structures in plant cells

Cell wall (cellulose, support), permanent vacuole (cell sap, keeps cell turgid), chloroplasts (photosynthesis, contain chlorophyll)

What is a prokaryotic cell?

A cell with no nucleus. DNA is a single loop in cytoplasm. Has plasmids (small rings of DNA). Example: bacteria. Typically 1-5 micrometres

What is a eukaryotic cell?

A cell with a true nucleus enclosed in a nuclear membrane. Animal and plant cells are eukaryotic. Typically 10-100 micrometres

Specialised cell: sperm

Streamlined shape, lots of mitochondria for energy, acrosome with enzymes to penetrate egg, long tail for swimming

Specialised cell: nerve

Long axon for carrying impulses, synaptic knobs with neurotransmitters, myelin sheath for insulation

Specialised cell: muscle

Lots of mitochondria for energy, protein fibres that contract

Specialised cell: root hair

Large surface area to absorb water and minerals from soil

How do you calculate magnification?

Magnification = image size / actual size. Rearrange: actual size = image size / magnification

Light microscope vs electron microscope

Light: resolution ~200nm, magnification up to x2000. Electron: resolution ~0.2nm, magnification up to x2,000,000. Electron shows sub-cellular detail like ribosomes

SEM vs TEM

TEM (transmission): 2D images, higher resolution, electrons pass through specimen. SEM (scanning): 3D images, lower resolution, electrons bounce off surface

Unit conversions for size

1 cm = 10 mm. 1 mm = 1000 micrometres. 1 micrometre = 1000 nanometres. To go smaller multiply by 1000. To go bigger divide by 1000

How to grow bacteria in the lab

Sterilise equipment (autoclave 121C). Pour agar into Petri dish. Inoculate with sterile loop. Tape lid (don't seal fully to prevent anaerobic pathogens). Incubate 25C in schools, 37C in industry

Area of a bacterial colony

Area = pi x r squared. Measure diameter, halve for radius

What is mitosis used for?

Growth, repair, and asexual reproduction. Produces two identical diploid daughter cells

Stages of the cell cycle

1) Interphase: cell grows, DNA replicates, organelles increase. 2) Mitosis: chromosomes line up, spindle fibres pull them apart, two nuclei form. 3) Cytokinesis: cytoplasm divides, two daughter cells form

What is a stem cell?

An undifferentiated cell that divides to produce more stem cells or specialised cells. Embryonic stem cells differentiate into any cell type. Adult stem cells are more limited (e.g. bone marrow makes blood cells)

What is differentiation?

The process where a cell becomes specialised for a particular function. In animals this happens early in development. In plants cells retain the ability to differentiate throughout life (meristems)

Therapeutic uses of stem cells

Treating paralysis, replacing damaged tissues, growing organs. Embryonic stem cells are controversial (destruction of embryo). Therapeutic cloning uses patient's own cells to avoid rejection

What is meristem tissue?

Found at root and shoot tips of plants. Contains undifferentiated cells that divide rapidly. Used to clone plants quickly and grow rare species to protect from extinction

What is diffusion?

Net movement of particles from higher concentration to lower concentration. Passive (no energy). Example: oxygen into blood in lungs

Factors affecting rate of diffusion

Concentration gradient (steeper = faster), temperature (higher = faster), surface area (larger = faster), distance (shorter = faster). Fick's Law: rate proportional to (SA x concentration difference) / thickness

What is osmosis?

Movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane. Passive process

Plant cells in different solutions

Pure water: turgid (swells, cell wall prevents bursting). Concentrated solution: plasmolysed (membrane pulls from cell wall). Animal cells in water: lyse (burst). Animal cells in concentrated solution: crenate (shrink)

What is active transport?

Movement of particles from low to high concentration (against gradient). Requires energy from respiration. Examples: root hair cells absorbing minerals, gut absorbing glucose

How is the small intestine adapted for absorption?

Villi and microvilli increase surface area. Single cell layer (thin wall). Good blood supply maintains concentration gradient. Lacteals absorb fats

Hierarchy of organisation

Cells > tissues > organs > organ systems > organism

Four types of animal tissue

Epithelial (covers surfaces), muscle (contracts), glandular (produces enzymes/hormones), connective (supports and holds together)

Digestive enzyme: amylase

Breaks starch into sugars. Made in salivary glands, pancreas, small intestine

Digestive enzyme: protease

Breaks proteins into amino acids. Made in stomach, pancreas, small intestine

Digestive enzyme: lipase

Breaks lipids into glycerol and fatty acids. Made in pancreas and small intestine

What does bile do?

Made in liver, stored in gall bladder. Alkaline so neutralises stomach acid. Emulsifies fats into small droplets increasing surface area for lipase

Role of hydrochloric acid in the stomach

Kills bacteria. Provides optimum pH for pepsin (protease) at pH 2. Denatures other enzymes

Food test: starch

Add iodine solution. Positive result: turns blue-black

Food test: glucose

Add Benedict's reagent and heat. Positive result: turns green/yellow/orange/red depending on concentration

Food test: protein

Add Biuret reagent. Positive result: turns purple

Food test: lipids

Add Sudan III. Positive result: forms a red layer

Components of blood: red blood cells

Carry oxygen. Biconcave shape (large SA). No nucleus (more room for haemoglobin). Contain haemoglobin which binds oxygen

Components of blood: white blood cells

Fight infection. Phagocytes engulf and digest pathogens. Lymphocytes produce antibodies and antitoxins

Components of blood: platelets

Cell fragments. Clot blood at wound sites to prevent blood loss and pathogen entry

Components of blood: plasma

Liquid part. Carries dissolved substances: CO2, glucose, amino acids, urea, hormones, antibodies, heat

Arteries

Thick muscular walls, small lumen, carry blood away from heart at high pressure, elastic fibres to stretch and recoil

Veins

Thin walls, large lumen, carry blood to heart at low pressure, have valves to prevent backflow

Capillaries

One cell thick, tiny, allow exchange of substances between blood and tissues

Structure of the heart

Four chambers: right atrium, right ventricle, left atrium, left ventricle. Right side pumps deoxygenated blood to lungs (pulmonary artery). Left side pumps oxygenated blood to body (aorta). Left ventricle thicker wall (higher pressure). Valves prevent backflow. Coronary arteries supply heart muscle

What is coronary heart disease?

Coronary arteries narrowed by fatty deposits (atheroma). Reduces blood flow to heart muscle. Treatments: stents (hold artery open), statins (reduce cholesterol), bypass surgery

Risk factors for cardiovascular disease

Smoking, high fat diet, lack of exercise, obesity, high blood pressure, diabetes, genetic factors, stress, excessive alcohol

How do lungs exchange gases?

Alveoli: large surface area, thin walls (one cell thick), moist lining for gas to dissolve, good blood supply maintains concentration gradient. O2 diffuses into blood, CO2 diffuses out

Plant tissue: epidermal

Covers and protects plant surfaces

Plant tissue: palisade mesophyll

Packed with chloroplasts, near top of leaf, main site of photosynthesis

Plant tissue: spongy mesophyll

Air spaces between cells allow gas exchange

Plant tissue: xylem

Carries water and minerals up from roots. Dead hollow tubes strengthened with lignin

Plant tissue: phloem

Carries dissolved sugars up and down (translocation). Living cells with sieve plates and companion cells

How is a leaf adapted for photosynthesis?

Broad and flat (large SA for light). Thin (short diffusion distance). Palisade cells near top (most light). Spongy mesophyll air spaces (gas exchange). Stomata on underside (gas exchange). Waxy cuticle (reduces water loss). Xylem and phloem in veins (transport)

What is transpiration?

Loss of water vapour from leaves through stomata. Creates transpiration stream pulling water up xylem. Faster in hot, dry, windy, bright conditions. Guard cells open and close stomata

What is translocation?

Transport of dissolved sugars and amino acids through phloem. From source (leaves) to sink (roots, growing tips, storage organs). Requires energy. Uses companion cells

Four types of pathogen

Bacteria: release toxins (e.g. Salmonella). Viruses: reproduce inside cells destroying them (e.g. measles, HIV). Fungi: hyphae penetrate tissues (e.g. rose black spot). Protists: parasites (e.g. malaria via mosquito vector)

How are pathogens spread?

Direct contact (STIs like HIV). Airborne/droplets (measles, flu). Water (cholera). Vectors (malaria by mosquitoes)

Disease: measles

Virus. Spread by droplets. Symptoms: fever, red rash. Complications: pneumonia, encephalitis. Prevention: MMR vaccination

Disease: HIV/AIDS

Virus. Spread by sexual contact, shared needles, blood. Attacks immune system (T helper lymphocytes). Late stage = AIDS. Controlled by antiretroviral drugs. No cure

Disease: Salmonella

Bacteria. Spread by contaminated food. Symptoms: fever, cramps, vomiting, diarrhoea from toxins. Prevention: vaccinating chickens, hygiene

Disease: gonorrhoea

Bacteria (STI). Spread by sexual contact. Symptoms: thick discharge, pain urinating. Treated with antibiotics but resistant strains emerging. Prevention: condoms

Disease: tobacco mosaic virus (TMV)

Virus affecting plants. Mosaic pattern of discolouration on leaves. Reduces photosynthesis. Spread by contact and contaminated tools

Disease: rose black spot

Fungus. Purple/black spots on leaves, leaves yellow and drop. Reduces photosynthesis. Spread by water and wind. Treated with fungicides and removing affected leaves

Disease: malaria

Protist (Plasmodium). Spread by mosquito vector (female Anopheles). Causes recurring fever, damages red blood cells and liver. Prevention: mosquito nets, insecticides, draining stagnant water

Body's non-specific defences

Skin (physical barrier), nose hairs and mucus (trap particles), trachea cilia and mucus (move pathogens up), stomach acid (kills pathogens), tears (contain lysozyme enzyme)

How does the immune system respond?

1) Phagocytes engulf and digest pathogens. 2) Lymphocytes produce specific antibodies that lock onto antigens. 3) Lymphocytes produce antitoxins. 4) Memory lymphocytes remain for rapid future response (immunity)

How do vaccinations work?

Inject dead or weakened pathogen. White blood cells produce antibodies. Memory lymphocytes made. On re-infection antibodies produced rapidly in large quantities. Herd immunity: enough people vaccinated so pathogen struggles to spread

What are antibiotics?

Drugs that kill bacteria (not viruses). Example: penicillin. Resistance develops through natural selection. MRSA is resistant. Slow resistance: complete courses, don't over-prescribe

Why are viruses hard to treat?

Viruses reproduce inside host cells. Drugs that damage viruses also damage host cells. Antivirals exist but are limited. Painkillers only treat symptoms

How are new drugs developed?

1) Discovery (plants, microorganisms, lab). 2) Preclinical testing (cells/tissues, then animals). 3) Clinical trials: Phase 1 (small group, safety), Phase 2 (larger group, dose), Phase 3 (large scale, efficacy). Double-blind: neither patient nor doctor knows who gets drug vs placebo. Peer review before approval

How are monoclonal antibodies produced?

1) Inject mouse with antigen. 2) Mouse lymphocytes produce antibodies. 3) Fuse lymphocyte with tumour cell = hybridoma. 4) Hybridoma divides rapidly producing identical antibodies. 5) Collect and purify

Uses of monoclonal antibodies

Pregnancy tests (detect HCG). Diagnosing disease (bind to specific proteins e.g. cancer markers). Treating cancer (carry drugs/radioactive substances directly to cancer cells). Research (locating specific molecules)

Problems with monoclonal antibodies

Side effects: fever, itching, low blood pressure. Not as widely used as hoped. More side effects than expected in trials

Equation for photosynthesis

Carbon dioxide + water --> glucose + oxygen. 6CO2 + 6H2O --> C6H12O6 + 6O2. Endothermic reaction. Occurs in chloroplasts

Limiting factors of photosynthesis

Light intensity (more = faster up to a point). CO2 concentration (more = faster up to a point). Temperature (too cold = slow, too hot = enzymes denature, optimum ~25-30C). Lowest factor is the limiting factor

Interpreting limiting factor graphs

Line rising = x-axis factor is limiting. Line plateaus = something else is limiting. Increasing other factors shifts plateau higher

What does the plant do with glucose?

Respiration (energy). Cellulose (cell walls). Amino acids (with nitrate ions for proteins). Lipids/oils (stored in seeds). Starch (storage, insoluble so doesn't affect osmosis)

How do greenhouses increase crop yields?

Control light (artificial lighting), temperature (heaters), CO2 (generators/paraffin heaters). Optimise all limiting factors. Equipment cost must be less than extra profit

Inverse square law for light intensity

Light intensity proportional to 1/d squared. Double the distance = quarter the light intensity

Equation for aerobic respiration

Glucose + oxygen --> carbon dioxide + water. C6H12O6 + 6O2 --> 6CO2 + 6H2O. In mitochondria. Exothermic. Continuous in all living cells

What is anaerobic respiration?

Without oxygen. Animals: glucose --> lactic acid. Plants/yeast: glucose --> ethanol + CO2 (fermentation). Less energy than aerobic. Used during vigorous exercise

What is oxygen debt?

After anaerobic respiration, lactic acid builds up. Extra oxygen needed to break down lactic acid in liver (converted back to glucose). Causes heavy breathing after exercise. Heart rate stays elevated

What is metabolism?

Sum of all chemical reactions in a cell/organism. Includes: protein synthesis, lipid synthesis, breakdown of amino acids (urea in liver), respiration, photosynthesis, glycogen synthesis/breakdown

Uses of fermentation

Bread: yeast ferments sugar, CO2 makes dough rise, ethanol evaporates in baking. Brewing: yeast ferments sugar in grains (beer) or grapes (wine) producing ethanol and CO2

How does exercise affect the body?

Heart rate increases. Breathing rate and depth increase. Blood vessels to muscles dilate. Glycogen in muscles broken down to glucose. If demand exceeds supply, anaerobic respiration begins

What is meiosis?

Cell division producing four genetically different haploid gametes. Two divisions. Chromosome pairs separate first, then chromatids. Crossing over and independent assortment create variation

Mitosis vs meiosis

Mitosis: one division, two identical diploid cells, growth/repair. Meiosis: two divisions, four different haploid cells, gametes. Mitosis = clones, meiosis = variation

What is DNA?

Deoxyribonucleic acid. Double helix polymer of nucleotides (sugar, phosphate, base). Four bases: A-T, C-G complementary pairing. Each gene is a section of DNA coding for a specific protein. On chromosomes in nucleus

Human genome project

Mapped all 20,000+ human genes. Benefits: identify disease-linked genes, targeted medicines, evolutionary relationships, forensics, personalised medicine

Sexual vs asexual reproduction

Sexual: fusion of gametes, meiosis, genetic variation, two parents. Asexual: no gametes, mitosis, clones, one parent. Some organisms do both (fungi, strawberries, daffodils)

How does a Punnett square work?

Shows all possible allele combinations from two parents. Parent gametes along top and side. Fill boxes with combinations. Calculate ratios/percentages of genotypes and phenotypes

Define: gene

A section of DNA that codes for a particular protein

Define: allele

A different version of a gene

Define: genotype

The combination of alleles an organism has (e.g. Bb)

Define: phenotype

The physical characteristic that is expressed

Define: homozygous

Having two identical alleles (BB or bb)

Define: heterozygous

Having two different alleles (Bb)

Define: dominant

An allele expressed when one or two copies are present (B)

Define: recessive

An allele only expressed when homozygous (bb)