2a+b Flashcards
Reproduction
Required to replace individuals in a population that have died through predation (being eaten), disease or old age.
Keeps the population of a species at a steady
number.
Sexual Reproduction
Usually involves 2 separate parents which produce sex cells called gametes.
Advantage - variation (can adapt to change)
Disadvantage - energy costs
Fertilisation
The nucleus of an egg (containing chromosomes) fuses with the nucleus of a sperm (which also contains chromosomes) to create a zygote (fertilised egg).
Gametes
Sex cells - sperm and eggs in animals, pollen and ovules in plants.
Sperm
Male gamete in animals. Tiny, streamlined and uses a tail to swim towards the egg.
Egg (ovum)
Female gamete in animals.
Much larger than the sperm as its cytoplasm contains a food store.
Unable to move by itself.
Zygote
A fertilised egg.
External Fertilisation
Sperms and eggs meet outside the body.
Found in aquatic organisms (that live in water) eg. frogs, fish.
Internal Fertilisation
Sperms are released inside the female reproductive system and fertilisation occurs inside the female.
Gametes need a watery environment to survive - they would dry out if released on land
Found in terrestrial (land living) organisms such as mammals, reptiles and birds.
Features of external fertilisation
Fertilisation is left to chance, so many gametes are produced.
Eggs have a tough outer coating
Developing embryos have a yolk sac as a food supply
There is little or no parental care - offspring look after themselves
Many young are produced as few survive.
Improving the chance of external fertilisation occuring
Parents are close together when gametes are released (eg. Frogs), Gametes are released into a nest (eg. Sticklebacks fish), Gametes are released at the same time (eg. Coral)
Embryo
Formed from a fertilised egg which divides repeatedly to form a ball of unspecialised embryonic stem cells. The embryo implants into the uterus lining.
Foetus
Once an embryo implants and starts to specialise, it is known as a foetus. It develops inside the uterus.
Amniotic fluid
Cushions the developing foetus and protects it from knocks.
Placenta
An organ which acts as a barrier to harmful substances.
It provides the developing foetus with food and oxygen from the mother’s blood.
Parental care
Offspring are looked after from birth.
Mammals produce milk to feed their young.
Fewer offspring are produced as most survive.
Flowers
Contain the sex organs of plants
Seeds
Formed after the ovule is fertilised during sexual reproduction in plants.
Contains a food store and an embryo, and is covered with a seed coat.
Ovary
Female part of the flower, containing ovules.
Stigma
Top section of the female part of the flower.
The pollen lands here.
Style
Connects the stigma to the ovary in flowers.
Stamen
The male part of the flower, made of a stalk (filament) and top section (anther).
Anther
The top section of the stamen, where pollen is made.
Petals
Brightly coloured flower parts that attract insects for pollination.
Sepals
Protect the unopened flower when it is a bud.
Pollination
The transfer of pollen from the anther of one flower to the stigma of another.
Wind pollinated flowers
Small, dull flowers eg. grasses
Reproductive parts hang outside the flower
Pollen is small and light
Insect pollinated flowers
Large colourful petals
Heavy, sticky pollen
Produce nectar to attract insects
Reproductive parts are inside the flower
Fertilisation (plants)
A pollen tube grows down through the style to the ovary.
The male nucleus enters the ovule and male and female chromosomes combine.
The ovule becomes a seed.
Fruit
The ovary wall (pericarp) turns into a fruit, which is a mechanism for seed dispersal
Asexual reproduction
One parent needed
Offspring are clones (exact copies) produced by mitosis.
Advantage - it is fast and energy costs are low
Disadvantage - no variation, so all have the same weaknesses and can’t adapt to change
Nectar
A sugary solution produced by flowers.
Attracts insects for pollination.
Seed dispersal
Spreading seeds away from the parent plant, using a fruit made from the ovary wall.
This avoids competition between the parent plant and seedlings for light, water and minerals.
Seed dispersal mechanisms
Wind - parachutes/fluff (dandelions and thistles)
Berries - eaten by animals and birds (blackberries, holly)
Hooks - attach to animal fur (burrs)
Shakers - shake seeds when stalks bend in the wind (poppies)
Exploding seed pods (peas, beans)
Helicopters - sycamore, maple
Germination
A seed comes out of dormancy.
The seed coat splits and a root comes out first, followed by a shoot.
Water, oxygen and warmth are needed for germination (not light)
Propagation
Producing new plants.
Either sexual (flowers, seeds, fruit) or asexual - runners, tubers etc
Asexual reproduction is fast and successful, but new plants are clones of the parent plant, so no variation.
Tubers
Underground food stores containing starch eg potatoes
They contain cells that can grow into new plants in the correct conditions.
Runners
Specialised horizontal stems with baby plants at the ends.
These root where they touch the soil and turn into new plants.
Strawberries, buttercups and spider plants produce runners.
Leaflets
Specialised leaf tissues that drop onto the soil and can grow into new plants. eg. Mexican hat plant
Bulbs
Underground food stores made of adapted stems with fleshy leaves.
New leaves grow from the centre of the bulb. eg. onions, garlic, daffodils, snowdrops.
Artificial Propagation
Propagation (producing new plants) that is carried out by humans. eg. stem or leaf cuttings and tissue culture.
This is faster than waiting for seeds to grow.
New plants are identical to the original parent plant.
Stem cuttings
Healthy shoots are selected and cut off the plant.
The lower leaves are stripped so they don’t rot, and so the plant doesn’t lose too much water through its leaves.
The cut stem is dipped in hormone rooting powder to encourage roots to grow.
The cutting is planted in a pot of damp soil and is covered with a plastic bag.
Roots take several months to develop.
Tissue culture
A new plant is made from a few cells taken from a donor plant
The cells are sterilised and grown on nutrient agar until a callus (clump of cells) forms.
The callus is transferred to agar containing hormones to encourage roots and leaves to grow.
It is used for high value plants such as orchids and is done is a lab
Hydroponics
Plants are grown without soil in nutrient solution containing nitrogen, phosphorous and potassium.
Used for growing salad leaves where space is limited, and to keep the leaves clean.
Uses of plants
Raw materials - timber, oils and fibres
Food, fuels, medicines
Aesthetics
Pharming
Raw materials
Wood - tree trunks are sliced into planks to form timber for building.
Plant fibres such as hemp and cotton are used to make paper, textiles and rope.
Seeds can be crushed to release oils, eg. sunflower oil
Food crops
Grown using agriculture.
Important crops include grains (eg. rice, wheat), beans, seeds, nuts, fruit, vegetables, herbs spices, tea and coffee.
Plants as fuels
Wood can be used as fuel, but it causes pollution (smoke) and deforestation.
Plant material can be used to make biogas and biodiesel, which is cleaner and more sustainable.
Medicine from plants
Aspirin (willow) - painkiller
Opium, morphine (poppy) - painkiller
Cannabidiol (cannabis) - used to treat epilepsy and MS
Aesthetics
The attractive appearance of plants.
Plants and flowers are used as decorations at weddings, funerals etc.
Wellbeing and plants
Walking in woodland and being outside amongst plants eg. gardening, is good for our health and wellbeing
Pharming
Genetically modifying a plant so that it produces a medicine.
DNA from a donor plant is inserted into a plant such as tobacco or rice.
The gene is copied as the plants make new cells and grow, and the medicinal protein is made.
The plant is harvested to extract the medicine.
Faster and cheaper than using bacteria.
Can be used to make vaccines and hormones.
It is controversial as genes could escape if modified plants breed with wild ones. (Pollen may escape).
Characteristics
Features such as eye colour, which are determined by proteins made by genes.
We inherit different combinations of chromosomes (and therefore genes) from our parents, making us unique.
Karyotype
The pattern made by breaking open the nucleus of a cell and lining the chromosomes up in matching pairs.
Fertilisation (human)
Occurs when the nucleus of an egg (23 chromosomes) combines with the nucleus of a sperm (23 chromosomes) to create a zygote (46 chromosomes).
Alleles
The different versions of a gene. eg. the eye colour gene has 3 alleles - brown, green and blue
The 2 chromosomes in a pair carry the same gene, but the alleles may be different.
Genotype
A 2 letter code indicating which alleles you have inherited from each parent (for a single gene) eg. BB
Capital letter = dominant allele, lower case letter = recessive allele.
Phenotype
Describes how a gene is expressed.
Often appearance (eg. eye colour) but not always (eg. blood type).
Monohybrid cross
Used to study how the alleles of 2 parents recombine in the offspring, for a single gene.
eg. BB x bb
Punnett square
A table used in a monohybrid cross to recombine gametes.
F1 generation
The offspring created in the original cross.
F2 generation
The offspring created by breeding 2 members of the F1 generation together.
Continuous variation
Variation that is controlled by many genes.
Produces a range of data. eg. height which can be displayed as a histogram.
Discrete (discontinuous) variation
Variation that is controlled by a single gene.
Data falls into separate categories eg. blood type, tongue rolling and is displayed as a bar chart.
Annual plants
Complete their lifecycle in one year. eg. poppies
They survive the winter as dormant seeds which germinate in the spring.
They are small, fast growing, produce many lightweight seeds and can grow on poor soils.
Perennial plants
Do not die after one year - they regrow from existing plants. eg. trees
They grow slowly, producing large seeds. They can grow very tall over time, and need fertile soil.
Plant growth curve
Shows the change in dry mass of a plant over its lifecycle.
Mass decreases during germination as the food store is used up, increases when the plant carries out photosynthesis and grows new tissue, then decreases as seeds are shed.
Requirements for plant growth
Warm temperatures
Water
Sunlight
Nutrients - nitrogen, phosphorous and potassium (NPK) dissolved in water
Nutrient deficiency (plants
If plants lack important nutrients, their leaves turn yellow and they have stunted growth (they don’t grow properly).
Nitrogen
Needed to build amino acids and proteins.
Phosphorus
Needed to build DNA and ATP (for cell reactions)
Potassium
Needed for photosynthesis
Human growth curve
Babies grow rapidly, then their growth rate slows down.
Boys and girls then have growth spurts during adolescence.
The steeper the graph, the faster the rate of growth.
Nature vs nurture
Your phenotype (characteristics) is determined by your genes and environment working together.
eg. you may inherit the alleles to be tall, but don’t grow tall due to a poor diet.
Twin studies
Identical twins separated at birth can be used to study the effects of environment on phenotype (as they are genetically identical)
Malnutrition
Occurs as a result of a poor diet lacking in essential nutrients.
Deficiency diseases
Occur if a particular important nutrient is absent from the diet.
eg. vitamin D deficiency - rickets; vitamin C deficiency - scurvy; vitamin A deficiency - blindness; lack of iron - anaemia
Birth defects
Occur as a result of damage to the parents’ DNA or the DNA of the developing baby during pregnancy.
Damaged DNA is unable to produce proteins that function correctly.
DNA can be damaged by chemicals (eg. Agent Orange, Thalidomide) or radiation (eg. following the Chernobyl disaster).
External factors
Factors in the environment which can affect our bodies. eg. weather conditions, food availability, water
Internal factors
Conditions inside our bodies eg. blood glucose level, body temperature
Optimum conditions
The best conditions for enzyme action.
Allow the body to work efficiently.
Homeostasis
Homeostasis refers to maintaining stable body conditions
Mechanisms to decrease body temperature
A rise in body temperature is detected by sensors (thermoreceptors) in our skin and blood vessels.
A signal is sent to the brain, which sends signals to sweat glands and blood vessels under the skin.
Sweat cools the skin as it evaporates.
Blood vessels widen, allowing hot blood to flow under the skin and lose heat by radiation.
Mechanisms to increase body temperature
A decrease in body temperature is detected by sensors (thermoreceptors) in our skin and blood vessels.
A signal is sent to the brain, which sends signals to hairs, muscles and blood vessels under the skin.
Hairs stand upright, and trap a layer of insulating air next to the skin.
Muscles contract rapidly, causing shivering, which generates heat.
Blood vessels narrow, preventing blood flow to the skin so less heat is lost.
Pancreas
An organ in the digestive system.
Contains receptors that detect changing levels of blood glucose.
Releases hormones to correct changes in blood glucose.
Hormones
Chemical signals that travel in the blood.
They target certain organs (which have the correct hormone receptors).
Insulin
A hormone released by the pancreas when blood glucose rises too high.
It targets liver cells, causing them to absorb glucose from the blood and store it.
This causes blood glucose levels to drop.
Glucagon
A hormone released by the pancreas when blood glucose falls too low.
It targets the liver, which releases stored glucose back into the blood.
This causes blood glucose levels to rise.
Type 1 diabetes
A serious disease caused when the body fails to produce insulin.
Blood glucose levels tend to fluctuate, and can get very high.
It is controlled by monitoring blood glucose levels and injecting insulin.
Type 2 diabetes
Insulin is still made, but the body stops responding to it and it has no effect, resulting in high blood glucose levels.
Caused by obesity and an unhealthy lifestyle.
Controlled by reducing sugar intake, exercise and eating healthy food.
