ppe pt3 (mar) Flashcards
entirety of paper 1 done (ends at flashcard 77) almost all paper 2
Give the differences between light and electron microscopes.
- Light microscopes are cheap to make, electron microscopes are expensive
- You can see the outlines of cells using a light microscopes
- You can see the finer details including organelles using an electric microscope
- Electron microscopes have a greater resolving power
- Electron microscopes have a higher resolution
What is the equation for magnification?
image size (actual size) / object (cell) size
How do you convert from micrometres (μm) to millimetres (mm)?
Divide by 1000.
What are the two main groups of cells?
- Eukaryotic cells (e.g. animal, plant)
- Prokaryotic cells (e.g. bacteria)
Where is DNA stored in eukaryotic cells?
The nucleus.
Where is DNA stored in prokaryotic cells?
In the plasmid (a loop of DNA)
Name the 5 organelles that animal and plant cells share.
- Cell membrane (semi-permeable, controls what enters and leaves)
- Nucleus (DNA)
- Mitochondria (respiration)
- Cytoplasm
- Ribosome (protein synthesis)
Name 3 organelles unique to plant cells.
- Chloroplasts (chlorophyll, photosynthesis)
- Cell wall (cellulose)
- Permanent vacuole (stores sap)
How do bacteria reproduce?
Binary fission.
Explain the process of making cultures with aseptic technique.
- Lift lid of petri dish towards flame (sterilising air)
- Put a drop of culture on agar and spread evenly
- Put drops of antibiotics on culture if needed
- Place a few bits of tape (allowing space for aerobic respiration between tape) on lid and dish to hold the lid closed
- Incubate at 25°C
- Measure size of cultures/areas with no bacteria with πr2
How many chromosomes does every human cell have?
23 pairs (46 in total), apart from gametes (eggs/sperm) which have only 23.
Describe the process of mitosis.
- The nucleus dissolves and genetic material is duplicated. The two sets of chromosomes move to different sides.
- Mitochondria, ribosomes and other organelles are duplicated.
- The cell divides, producing two genetically identical diploid cells (cells with 23 pairs of chromosomes).
- New nuclei are formed.
What is a stem cell?
A cell that hasn’t specialised yet.
Where are stem cells found?
- Animal embryos
- Plant meristems
- Bone marrow (this stem cells can only specialise into blood cells)
Name and explain one process used to make more stem cells.
Embryonic cloning: These embryo clones can be made of a person to harvest stem cells from.
- The developing animal embryo is then split apart many times before the cells of the embryo become specialised
- This forms many separate embryos that are genetically identical
- These cells can be used to treat conditions without the cells being rejected
What else can cloning be used for?
The preservation of species or producing crops with desired traits.
Define diffusion.
Diffusion is the movement of particles from an area of high concentration to low concentration. It doesn’t require energy and so, passive.
Define osmosis.
The movement of water particles from area of high concentration to low concentration through a semi-permeable membrane to balance the concentrations of a solution inside/outside a cell.
Name 3 things that can increase the rate of diffusion.
- The difference in concentrations
- Surface area
- Temperature
Describe the osmosis practical.
- Weigh then place identical potato cylinders in sugar solutions of varying concentrations
- After a set time (24 hours) remove excess water and reweigh the cylinders
- Calculate the percentage change in mass using the following equation:
(final mass - initial mass / initial mass) * 100 - Plot the percentage change in mass against concentrations. Where the line of best fit crosses the x-axis is which concentration should result in no osmosis. Meaning, the concentration of sugar in the sugar solution is the same as the concentration of sugar in the potato cylinder.
Define active transport.
The movement of particles through a membrane via carrier proteins. This requires energy because the particles need to move against the concentration gradient.
What is the order of organisation?
Cell -> tissue -> organ -> organ system
Explain the digestive system.
- Teeth breaks down food mechanically. Saliva contains amylase, an enzyme which breaks down carbohydrates (starch and sugar)
- It travels down the esophagus to the stomach, containing hydrochloric acid and enzymes (amylase, lipase and protease) that chemically break down the food.
- The live produces bile which is stored in the gall bladder; it’s used in the small intestine to emulsify lipids forming droplets and increasing their surface area
- The pancreas secretes amylase which breaks down starch into glucose in the small intestine
- Water is absorbed into the bloodstream in the large intestine
- Nutrients like glucose are absorbed into the bloodstream by the villi in the small intestine (starch is too large)
What is an enzyme?
Special proteins that act as biological catalysts. They aren’t ever used up.
They’re specific and so only break down substrates that fit their active site (‘lock and key’ principle)
Name 3 enzymes and what they breakdown.
- Carbohydrase breaks down carbohydrates into simple sugars (amylase breaks down starch into glucose).
- Protease breaks down proteins into amino acids.
- Lipase breaks down lipids into glycerol and fatty acids.
What increases enzyme activity?
- Temperature (until the enzyme denatures)
- pH (unless its too high or low, in that case it denatures)
Define optimum conditions.
The conditions for max rate/activity.
Explain the enzyme practical.
- Mix amylase with starch in a test tube and start timer
- Remove a few drops from the mixture every 10 seconds and add to iodine within a dimple tray
- Record the time taken for no starch to be detected (the iodine in the dimple tray remains orange)
- Repeat at different temperatures with different pH buffer solutions added.
- The optimum conditions are between the two shortest times.
List and explain the food tests.
- Starch: turns iodine from orange to black
- Sugars: turns benedict’s solution from blue to brick red when heated
- Protein: turns biuret’s reagent from blue to purple
- Lipids: turns cold ethanol cloudy
Explain the respiratory system.
- Air passes through the trachea and the bronchi to the bronchioles. Within the bronchioles are the alveoli.
- The oxygen diffuses into the blood vessels around it, and CO2 & water diffuses out of the plasma of the blood.
(Alveoli have large surface area to allow gas exchange to occur at a fast rate.) - Oxygen diffuses into the bloodstream and binds to the haemoglobin in red blood cells to be transported.
What is a double circulatory system?
The heart; blood enters the heart twice every time it’s pumped around the body (hence it circulates twice).
Name the parts of the heart on the right side of the heart.
- Vena cava (blood from the body enters through here into right atrium)
- Valve (preventing backflow above right ventricle)
- Pulmonary artery (pumps blood to lungs)
Name parts of the heart on the left side of the heart.
- Pulmonary vein (blood from the lungs enters through here into the left atrium)
- Aorta (blood enters left ventricle and is pumped through here to the rest of the body)
Explain how blood travels in the heart.
- Blood enters through the vena cava from the body into the right atrium
- It’s passed through a valve into the right atrium where it is pumped through the pulmonary artery to the lungs to be oxygenated
- Blood then re-enters through the pulmonary vein into the left atrium and enters the left ventricle to be pumped through the aorta to the rest of the body
Give 2 differences between the right and left side of the heart.
- The left side has thicker walls due to the greater pressure needed to pump blood around the entire body (compared to only the lungs)
- A group of cells are in the walls of the right atrium that create electrical pulses causing the heart to contract
If the above doesn’t work in a person, an artificial pacemaker can be used.
Define artery and give the features of it.
Carrier of blood away from the heart. It has thick walls and thin lumen to withstand high pressure.
Define capillary.
One cell thick walls to allow fast diffusion between blood and cells.
Define vein.
Carrier of blood back to the heart. It has thin walls and wide lumen, valves to prevent backflow (can be replaced with artificial ones if faulty).
What is CHD?
Coronary heart disease; when the artery supplying blood to the heart becomes blocked by the build up of fatty deposits; restricting blood flow. It can trigger strokes and heart attacks.
How do doctors treat CHD?
- Stents can be inserted to open up the vessel.
- Statins are drugs that can reduce these fatty deposits.
What is in the blood?
- Red blood cells (to carry oxygen around)
- White blood cells (to fight infection)
- Platelets (for clotting)
- Plasma (to carry everything else blood needs to)
What are the types of diseases?
Non-communicable and communicable disease.
What are non-communicable diseases caused by?
A factor inside the body.
Give examples and risks of non-communicable diseases.
- Diabetes: obesity and poor diets increase risk
- CHD: Poor diet, smoking and a lack of exercise
- Liver disease: alcohol increases risk
- Lung disease or cancer: smoking
- Cancer: carcinogens
What is cancer (and what are the 2 types of tumour)?
An autoimmune condition resulting from genetic mutation causing cells to multiply uncontrollably - tumour.
A benign tumour doesn’t spread.
A malignant tumour spreads through the body.
Explain plant structure.
- Leaves: in charge of photosynthesis and gas exchange. Water evaporates out.
- Xylem: continuous tubes that carry water and dissolved mineral ions upwards (<- transpiration, unidirectional. Rate increased by increased air movement, temperature and decreased humidity).
- Roots: water enters through osmosis, mineral ions by active transport.
- Flower: reproductive organs
- Meristem: stem cell production
- Phloem: tubes of cells that carry sugars and other nutrients to where needed (<-translocation, bidirectional).
What is needed for protein synthesis? (in plants)
- Nitrates; without it there is stunted growth
What is chlorosis?
- A magnesium deficiency (magnesium is used to make chlorophyll and is taken from the soil)
- It shows up through yellow leaves and stunted growth due to less chlorophyll
Explain leaf structure from top to bottom.
- Waxy cuticle: waterproof to stop water loss from top of leaf
- Upper epidermis: transparent to let light through
- Palisade mesophyll: most photosynthesis takes place here
- Spongy mesophyll: has gaps to facilitate gas exchange (large surface area)
- Vein/vascular bundle: xylem & phloem
- Lower epidermic: bottom of leaf
- Stomata: holes in lower epidermic to allow gases in/out, including water
- Guard cells: change size to control rate of gases entering and exiting through stomata
What are communicable diseases caused by?
A pathogen (a microorganism that causes disease e.g. bacteria, viruses, fungi and protists).
How do viruses reproduce?
They insert genes into cells which causes them to produce more copies.
Give 2 examples of viruses.
- Measles (Rash spread by droplets)
- HIV (an STD/STI that causes AIDS - compromised immune system)
How does bacteria infect?
Releases toxins into your body that damages cells.
Give 2 examples of bacteria.
- Salmonella (from undercooked food; food poisoning.
- Gonorrhoea (STD, causes yellow discharge).
Does fungi affect plants or humans more?
Plants.
What is a protist (and provide an example)?
A single-celled organism, e.g. malaria; caused by a protist that infects red blood cells. Mosquitoes are the vector.
Name some plant disease.
- Rose black spot (caused by a fungus) which causes leaves to fall off (black spots appear on the leaves).
- Tobacco mosaic virus, which discolours leaves due to less chlorophyll, causing stunted growth.
Explain the human defence system.
- Skin stops pathogens from entering
- Nose/trachea traps pathogens with mucus
- Acid and enzymes within the body kill pathogens
Explain the plant defence system.
- Cell wall, waxy cuticle and bark are barriers
- Antibacterial chemicals, poison/thorns deter other organisms
If a pathogen passes the human defence system, how will the body next defend itself?
Using white blood cells.
Name 2 white blood cells the body uses to defend itself.
Lymphocytes: they produce antitoxins that neutralise toxins made by pathogens and antibodies that bind to the antigen of a pathogen (the antibodies must fit to the antigen or they won’t work). These together stop viruses from infecting cells, and cause them to clump together.
Phagocytes will then ingest the clumped pathogens.
NOTE: if lymphocytes don’t recognise the antigen, the lymphocytes will make many different shaped antibodies until one fits. Once it does, it’ll be stored in your lymph nodes, giving you immunity.
What is the purpose of a vaccine?
A vaccine introduces a dead/inert version of a virus into your body, so you can gain immunity without becoming ill.
Explain the purpose and production of antibiotics.
Antibiotics kill bacteria (only). It’s difficult to make them target specific bacteria; but we need to as they may damage our cells or other ‘good’ bacteria and as bacteria mutate they can become strong and resistant to antibiotics, so you mustn’t take too many and take the entire course of antibiotics.
Many drugs used to come from nature but, they’re typically synthetic now (and expensive to develop).
Explain synthetic drugs.
Synthetic drugs are expensive antibiotics that are man-made. They’re put through trials to assess efficacy, toxicity and dose. They’re tested on cell tissue, animals, then lastly humans.
Human trials are typically blind trials: the test group are given the drug and the control group is given placebo, without either party being aware.
There are also double-blind trials where even the doctor don’t know which party has placebo and which has the drug, eliminating bias.
What are monoclonal antibodies?
Antibodies that are produced by clones of a cell that produces it.
How do you make monoclonal antibodies?
- Lymphocytes from mice combined with tumour cells to make hybridoma
- Hybridoma multiply, producing lots of same antibody
Give one pro and one con of the use of monoclonal antibodies.
Monoclonal antibodies have many uses, such as medical diagnosis and pathogen detection. However, unfortunately, the side effects are worse than doctors anticipated.
What is the word and chemical equation for photosynthesis?
water + carbon dioxide -> glucose + oxygen
6H2O + 6CO2 -> C6H12O6 + 6C2
What is the rate of photosynthesis increased by?
- Increasing temperature
- Increasing light intensity
- Increasing CO2 concentration
These factors can all be optimised until the limiting factor is the max amount of chlorophyll the plant can have.
What is glucose used for?
- Respiration
- Making starch/fat to store energy
- Making cellulose
- Making amino acids for proteins
Explain the limiting factor practical.
- Cut pondweed stem and put in an inverted measuring cylinder, filled with water (add sodium hydrogen carbonate to it to provide CO2). Measure distance from the light source.
- Allow it to acclimatise first, then count the amount of bubbles produced by the weed in 1 minute (not very accurate)
- Repeat at different distances from the light source
Light intensity and distance follow an inverse square law: distance *2 = light intensity /4
Every cell apart from red blood cells has what?
The mitochondria, the powerhouse of the cell. It’s where respiration takes place.
What is respiration useful for?
Providing energy for chemical reactions, warmth and movement.
What is aerobic respiration?
Respiration with oxygen.
glucose + oxygen → water + carbon dioxide
C6H12O6 + 6CO2 → 6H2O + 6CO2
What happens to the body during exercise?
Heart rate and breathing rate increase to increase blood flow, supplying more oxygen and glucose to enable muscles to contract. The body also carries out anaerobic respiration, creating oxygen debt. The lactic acid produced is broken back down into glucose by the liver using oxygen. Also arteries supplying blood to muscles widen.
What is anaerobic respiration?
Respiration without oxygen.
- In the body:
glucose ⇾ lactic acid
C6H12O6 → 2C3H6O3
- In plants and fungi:
glucose ⇾ ethanol + carbon dioxide
What is metabolism?
The sum of all chemical reactions in a cell/organism.
For example:
- glucose ⇾ starch, glycogen and cellulose
- fatty acids ⇾ lipids
- respiration
- breakdown of excess proteins ⇾ urea
What is homeostasis?
An organism’s ability to regulate its internal conditions, so crucial reactions can happen at optimal rates.
It’s needed for: blood glucose concentration, internal temperature and water levels.
What is the nervous system?
The central nervous system (brain and spinal cord) and the peripheral nervous system (all other nerves).
Explain the process of the nervous system.
- A receptor (e.g. skin) detects a stimulus (e.g. heat)
- An electrical signal travels through the spine through sensory and relay neurones (nerve cells)
- The signal crosses the synapse between the neurones using a neurotransmitter chemical.
- Once the brain receives the signal, it can make the conscious decision to act.
- The signal then goes back to an effector (e.g. a muscle) via motor and relay neurones so you can respond.
What is the reflex arc?
When the signal bypasses the brain, it’s much quicker than the process of the nervous system.
What are glands?
Effectors, which secrete chemicals in response to certain hormones.
What is the reaction time practical?
- Drop the ruler between first finger and thumb
- Measure distance fallen before caught, repeat and calculate mean
- Repeat steps 1 and 2 after subject has drank an energy drink (which would hypothetically increase reaction time)
- Once you’re done with the results, you could use s = 0.5*a*t2
What are the 4 parts of the brain needed to be known?
- Cerebral cortex (part on top)
- Pituitary gland (part in middle)
- Cerebellum (on the side)
- Medulla oblongata (on the bottom)
What is the cerebral cortex responsible for?
Higher functions:
- Memory
- Speech
- Problem-solving
What is the cerebellum responsible for?
Motor skills:
- Movement
- Balance
- Coordination
What is the medulla oblongata responsible for?
Unconscious actions:
- Heart and breathing rate
- Signals to adrenal glands to release adrenaline
What is an MRI scan?
Magnetic Resonance Imaging, which allows doctors to see brain activity without surgery. Issues with the brain are difficult/impossible to treat safely.
What makes up the eye?
From the outside in….
- Cornea
- Iris
- Pupil (hole in the iris which changes size depending on the light intensity hitting the eye)
- Lens
- Suspensory ligaments and ciliary muscles
- Retina
- Optic nerve (leads to brain)
- whole outside/outline thing: Sclera
What is accommodation, and how does it work?
It’s the eye’s ability to change the shape of the lens in order to focus light that comes from different objects at different distances away, on the retina.
- When something is far, the ciliary muscles relax and the suspensory ligaments tighten, creating a thin lens.
- When something is close, the ciliary muscles tighten and the suspensory ligaments relax, creating a thick lens.
Explain how the retina detects light and colour.
Using rods and cones.
- Rods only detect light intensity
- Cones sensitive to red, blue or green wavelengths of light provide colour information
These signals sent by the rods and cones travel to the brain via the optic nerve.
What are the terms for short and long-sightedness and how can they be treated?
Myopia is short-sightedness and hyperopia is long-sightedness. Both can be treated with glasses, contact lenses or laser eye surgery.
What is thermoregulation?
The regulation of blood temperature (ideal temp: 37°C), regulated by effectors.
Explain thermoregulation when too hot.
- The brain detects blood temp is too high and sends nervous and hormonal signals to effectors
- Sweat glands produce water which evaporates, taking away heat
- Vasodilation takes place (blood vessels dilate), allowing more blood flow around the body. The skin flushes, making the air hot and your body cool through radiation.
Explain thermoregulation when too cold.
- Hairs stand on end to trap air, acting as a layer of insulation.
- Shivering; the muscles produce more heat
- Vasoconstriction (the very opposite of vasodilation effects)
What is the endocrine system?
The system of glands that secrete hormones to send signals to effectors, transported via blood (slower than the nervous system).
What is the endocrine system made up of?
- Pituitary gland (sends signals to the other glands)
- Thyroid (controls growth, metabolism and more)
- Pancreas (secretes insulin and glucagon to control blood sugar
- Adrenal glands (release adrenaline)
- Ovaries (release eggs and secrete hormones) and testes (produces sperm)
What will the body do to control blood glucose levels?
If it’s too high:
- Pancreas secretes insulin, which causes glucose to move from the bloodstream into cells to be used for respiration
- Excess glucose is converted into glycogen as an energy store
If it’s too low:
- Pancreas secretes glucagon, which causes liver and muscles to convert glycogen back into glucose (this is an example of a negative feedback loop)
What is the difference between type 1 and type 2 diabetes?
In type 1 diabetes, the pancreas can’t produce enough insulin and injects of insulin are needed to treat it.
In type 2 diabetes, cells don’t absorb glucose as they should, so you need to be careful with your diet. Obesity increases the risk of getting this.
How does the body control water and nitrogen levels?
- Water is lost through exhalation, sweating and urinating
- Excess water is removed from blood by kidneys to the bladder where its mixed with urea to make urine
- Urea contains ammonia (NH3) from amino acids obtained from excess proteins broken down in the liver.
What happens if there’s too much/little water in your body?
If there’s too much, water will move into cells by osmosis. Cells become turgid and could burst.
If there’s too little, water moves out of cells by osmosis. Cells become flaccid.
Name a job of the kidneys (that isn’t managing water levels).
Filtering out glucose and useful minerals and ions from the blood for the body to use.
Explain the cycle the kidneys use to control water levels.
- ADH from the pituitary gland causes tubules in kidneys to reabsorb more water into the bloodstream when water levels are too low
- If the water levels are too high, less ADH is made, so more water is sent to the bladder to leave the body as urine
^ negative feedback cycle
What is the danger if your kidneys don’t work properly, and how can it be treated?
If your kidneys don’t work properly, ammonia/urea build-up could occur, which is poisonous. To treat this, you can take part in dialysis, which filters the blood using a machine.
What is FSH?
The Follicle Stimulating Hormone from the pituitary gland which causes an egg to mature within a female, and the ovaries to produce oestrogen.
What is oestrogen?
A hormone which causes the uterus lining to thicken, and it inhibits FSH so no more eggs mature until the next menstrual cycle. It also causes the pituitary gland to secrete LH.
What is LH?
The Luteinising hormone, which causes an egg to be release, which starts to travel towards the uterus. A sperm cell can fertilise it while in the oviduct.
What is progesterone?
A hormone secreted by the ovaries which maintain the uterus lining.
List types of contraception.
- FSH-inhibiting pills so no eggs mature
- Progesterone injection/implant (convenient) to stop eggs being released
- Condom/diaphragm to stop sperm entering vagina
- IUD (copper coil) which stops egg embedding in lining
- Avoiding sex for some time after egg is released
- Clamping oviduct or having a vasectomy (cutting sperm tubes)
Give 2 types of fertility treatments.
- FSH/LH injections - simple!
- IVF (in-vitro fertilisation) - hard/expensive
Explain the process for IVF treatment and some cons.
- Eggs are collected after inducing release with LH to be fertilised in a lab
- Viable embryos are inserted back into a female’s uterus.
The success rate is very low, and it risks more than one baby being born. It is also physically and mentally stressful for the patient.
What are the adrenal glands?
Glands attached to the top of the kidney which release adrenaline into your body, which increases blood flow and breathing rate, preparing you for ‘fight or flight’.
What is thyroxine?
A hormone secreted by the thyroid which controls your body’s metabolic rate. If it’s too low, the hypothalamus in the brain releases TRH which causes the pituitary gland to release TSH which causes the thyroid to release more thyroxine.
^ negative feedback cycle
List 3 plant hormones.
Gibberellins, ethene and auxins.
What do gibberellins do?
- Induces germination
- Promotes flowering
- Increases fruit size
What does ethene do?
Causes ripening, converts starch into sugar and naturally given off by ripe fruit.
What do auxins do and give some uses.
It promotes growth. It can be used as weedkiller, as rooting powder and for promoting growth in tissue cultures.
Explain phototropism and geotropism.
Phototropism is when the shaded side of a plant elongates quicker than the side with sunlight on it, causing the shoot to bend towards the sun. This is because sunlight destroys auxins.
Geotropism is when auxins gather on the bottom of roots, where it inhibits growth - meaning it grows downwards instead.
Describe the practical which allows you to observe geotropism.
- Place seeds on damp cotton wool in a petri dish stood on an edge.
- Turn 90 degrees after a few days to observe geotropism in roots.
*You can also do a practical to observe phototropism by observing plants in different light over the course of a week.
How do animals and plants reproduce?
Animals only reproduce sexually while plants can reproduce sexually (pollen and egg) and asexually.
(Malaria parasites and some fungi can do both too)
Explain meiosis.
How gametes are made:
- Chromosomes in a diploid cell are copied (23 pairs).
- Similar chromosomes pair up and genes are swapped between them.
- Cell divides to produce two diploid cells.
- These cells divide again to produce 4 haploid cells or, gametes.
These are genetically different from parent cells.
How does asexual reproduction take place?
Mitosis, creating identical offspring.
What is an advantage of sexual reproduction?
Offspring can become better adapted to the environment.
What is an advantage of asexual reproduction?
Only one organism needed to reproduce.
Define genome.
The entire genetic code in an organism.
What is DNA?
A double helix polymer - stores genetic code.
Define gene.
Section of DNA that codes for a protein.
What is a genotype?
An organism’s specific genetic code.
Define phenotype.
How a genotype is expressed in physical characteristics.
Why is mapping out genes useful?
It allows us to identify causes of disorders.
What are nucleotides?
What DNA is made up of. Nucleostides consist of sugar, a phosphate group and a base.
What are the 4 bases?
A, T, C and G.
They match up: A&T, C&G.
What codes for an amino acid?
Every 3 bases.
Explain protein synthesis.
- Code is copied by mRNA (transcription) then taken to ribosome
- Ribosome assembles amino acids into polypeptides then proteins (translations)
- The proteins are folded into shape
What is mutation?
A change to the sequence of DNA bases in an organism. Sometimes inherited, sometimes not.
They can be harmless, or causes diseases e.g. cancer.
Some mutations also change how certain genes are expressed.
List some causes of mutation.
- Ionising radiation
- Chemical mutagens
- Infectious agents
- Spontaneous growth
Name 3 different ways DNA sequences can change through mutation.
- Subtitations; base is swapped for another
- Deletions; base is deleted from sequence
- Insertion; random base added to sequence
How are characteristics determined?
By the type and quantity of proteins synthesised. Most are a result of two or more genes interacting.
What are alleles? (and how are dominant and recessive alleles expressed)
Different versions of the same gene.
Dominant alleles are expressed even when the genotype contains a recessive allele. There must be no dominant allele in order for a recessive allele to be expressed in the phenotype. There is a 25% chance that the recessive allele will be expressed.
What are homozygous and heterozygous alleles?
- Homozygous alleles are when the allele pair has 2 dominant or recessive alleles.
- Heterozygous alleles are when the allele pair has 1 dominant and 1 recessive allele.
What is a punnet square/how does it work?
A way to calculate the probability of a baby having a certain gene. Works like this:
// B | b
B BB Bb
b Bb [bb] -> 25% chance of little b gene
Capital letter = dominant allele, lowercase letter = recessive allele
What are polydactyly and cystic fibrosis, and what are they caused by?
Polydactyly is when we have extra fingers or toes and is caused by a dominant allele.
Cystic fibrosis is caused by a recessive allele (parents are carriers or have CF).
XX chromosomes vs. XY chromosomes?
XX chromosomes makes you a female, XY chromosomes makes you a male.
What is variation?
The result of both genetic and environmental factors.
Explain Darwin’s theory of evolution.
- Random mutations results in variation
- Some organisms better adapted to environment
- These compete and those better adapted are more likely to survive and can reproduce
- Over time these desirable characteristics are more pronounced
Explain Lamarck’s theory of evolution.
Mutations/adaptations are a result of environment affecting characteristics inherited by offspring: not random.
What is antibiotic-resistant bacteria?
- Bacteria used as evidence for Darwinian evolution
- If not all bacteria killed, those most resistance will reproduce
- Hence why you must complete the full course of antibiotics
Why was Darwin’s theory of evolution controversial?
- At the time, it didn’t have lots of evidence
- It refuted the idea of divine creation by suggesting everything is random
- Lack of ways to explain how variety and inheritance happened
What was used recently as evidence for Darwinian evolution?
Antibiotic-resistant bacteria. If not all bacteria dies, those most resistant will reproduce which is why you must complete the full course of antibiotics.
What classifies organisms as a species?
Whether they can produce fertile offspring.
What is selective breeding?
The breeding of organisms that have desired characteristics to produce offspring in which they are more pronounced.
What is genetic engineering?
The insertion of a gene into an organism’s genone so it synthesises a specific protein to achieve a desired characteristic.
What is the process of genetic engineering?
- Desired gene is cut from another organism’s DNA using enzyme
- Gene inserted into a vector (e.g. bacteria, plasmid or virus)
- Vector inserts gene into cells of another organism in development
- Organism develops with desired characteristic; due to every cell synthesising that specific protein
Give some examples of genetic engineering being useful.
- Rice plants have been GE’d to be flood resistant so freuquently flooded countries have more rice
- Soybeans have been GE’d to have more fatty acids to give consumers a better diet
- Some crops have been GE’d to be resistant to common diseases e.g. tobacco mosaic virus.
What do organisms compete for within an ecosystem?
- Food
- Water
- Space
- Light
- CO2/O2
- Mates
What is interdependence?
Organisms depending on each other for survival. When this happens, a community is formed.
What are abiotic factors?
Non-living factors (e.g. light, temperature, moisture, soil pH, CO2 and O2 concentration)
What are biotic factors?
The impact of other organisms on an ecosystem (e.g. food, predators/prey and pathogens)
Explain sampling.
- Place quadrat in random positions in an area (ideally 10% of an area, using a random number generator to choose locations)
- Count the number of chosen organism in each, calculate mean then multiply by total area to get an estimate for population
- Moving it along a transect allows you to observe changes in population density over a distance
What is a food chain?
A chain which shows the direction of biomass transfer between organisms.
Producer (biomass producer) ⇾ primary consumer (herbi/omni) ⇾ secondary consumer (carni/omni) ⇾ tertiary consumer (carni/omni)
What is an apex predator?
Predators always at the top of the food chain with no natural predator.
What is a trophic level?
The position of an organism on a food chain.
All life is based on what?
Carbon. It’s recycled when an organism dies and decomposes and as they excrete CO2 while alive (bacteria do this too).
Explain the water cycle.
(8 steps)
- Precipitation, water droplets in clouds get heavier they fall as rain, snow or hail.
- Percolating, water trickles through gaps in soils and rocks.
- Transpiration and respiration, loss of water vapour from plants and animal directly to the atmosphere.
- Some of the water becomes surface run-off, which runs into the ocean.
- Evaporation, the sun heats the earth’s surface and water is turned from a liquid into water vapour, forming warm moist air
- 3&5 (transpiration, respiration and evaporation) produce water vapour
- Condensation, as moist air rises it cools, water vapour condenses back into liquid water droplets producing clouds.
- The water cools and the cycle starts again.
What is decomposition?
The breakdown of dead matter.
What is the rate of decomposition affected by?
- Temperature - Chemical reactions in microorganisms work better in warmer conditions. If it’s too hot/cold, the enzymes will denature/become inactive
- Moisture - Makes it easier for the microorganisms to digest the organic matter and not dry out
- Oxygen availability - Although some microorganisms respire anaerobically, many respire aerobically.
How do you calculate the rate of decay?
change in mass (g) / time (days) = rate of decay (g/day)
When decomposers break down compost, what happens to it?
The compost becomes warmer due to the respiration of decomposers, releasing energy in the form of heat.
What are biogas generators, and how do they work?
Decomposers. When bacteria decompose anaerobically, they produce methane and smaller amounts of CO2, which can be collected as biogas which is burned to release energy. This can reduce the waste that ends up in landfill as it repurposes waste.
What are the 3 types of environmental changes?
- Seasonal (temperature, climate)
- Geographical (soil structure or pH, altitude, water availability)
- Human interaction (positive and negative (e.g. global warming vs. rain forest maintenance))
What is global warming?
The gradual increase of the earth’s surface temperature. This results in changes in climate, the melting of ice caps, raising of sea levels and habitat loss - which makes species extinct or endangered.
What is biodiversity?
The variety of all the different species of organisms on earth or within an ecosystem.
How do humans reduce the amount of land available for animals and plants?
By building houses and factories, and dumping waste in landfills.
What is the main reason for the destruction of peat bogs?
To produce cheap compost (fertiliser), and generate electricity.
What happens when peat is extracted and used for compost?
It reduces biodiversity and releases CO2.
Why is the destruction of peat bogs a problem?
It reduces the variety of animals and plants and releases CO2 into the atmosphere, contributing to global warming.
What are peat bogs and peat lands rich in?
Dead plant materials and CO2.
Why have many gardeners stopped buying compost made with peat?
It reduces biodiversity and contributes to climate change.
What is the main impact of human activity on land use?
Reduction of habitat.
What is a peat bog?
A massive carbon store (so they release massive amounts of CO2 when burnt) with a unique ecosystem, and therefore habitats for unique organisms. They take thousands of years to regrow.
What is a biofuel?
A fuel produced from a living or recently living organism through burning.
Why does large scale deforestation take place in tropical areas?
To provide land for farming cattle, rice fields and growing crops for biofuel.
Name 4 positive effects of human interaction on an ecosystem.
- Reducing deforestation and CO2 emissions.
- Breeding programs and protection/regeneration of rare habitats.
- Reintroduction of field margins (land between crops and field boundary).
- Recycling resources.
Name 4 negative effects of human interaction on an ecosystem.
- Global warming and deforestation.
- Animals and plants becoming endangered due to reduction in habitat.
- Large 40 acre fields growing one crop.
- Dumping waste in landfill areas.
What is land pollution caused by?
Landfills and toxic chemicals.
What is air pollution caused by?
Smoke and acidic gases.
What is water pollution caused by?
Sewage or toxic chemicals in bodies of water and fertiliser.
What is land needed for?
Building, quarrying, farming and disposing of waste.
What does a pyramid of biomass indicate?
How much biomass is transferred between trophic levels.
How do you calculate the percentage of biomass absorbed by the above level?
% absorbed = (biomass at n+1 level / biomass at n level) * 100
Why is biomass lost at each level?
Because not all of it is being consumed/absorbed at each level, and organisms losing it while they’re alive via excretion.
What is the concern with food security?
There are changing diets and growing environments, fuel and energy prices, cost of farming and conflicts.
To fix this, farmers are trying to farm more efficiently; increasing biomass input while reducing wasted biomass. Genetically modified crops can increase yields too.
What is sustainable fishing?
Fishing which ensures that fish aren’t caught faster than they can breed, so populations remain consistent.
This is done by catching with nets with large holes, so juvenile fish can escape and breed.
