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Biology Paper 2 - 2023 Predicted, https://quizlet.com/gb/693813768/biology…
Biology Paper 2 - 2023 Predicted
Food chains
A simple way to show the feeding interactions between the organisms in a community is with a food chain
A food chain shows the transfer of energy from one organism to the next
The source of all energy in a food chain is light energy from the Sun
The arrows in a food chain show the transfer of energy from one level of the food chain to the next
Position in food chain -> Organism example -> Explanation
Producer -> Grass seed -> Makes its own food using energy from sunlight in photosynthesis
Primary consumer -> Vole -> Eats the producer
Secondary consumer -> Barn owl -> Eats the primary consumer
Investigating ecosystems
Ecology is the branch of biology that studies the distribution and abundance of species, the interactions between species, and the interactions between species and their abiotic environment
You need to know how ecologists determine the distribution and abundance of species in an ecosystem using quadrats and transects
You need to understand how they use quadrats and transects in order to do this
Quadrats are square frames made of wood or wire - They can be a variety of sizes eg. 0.25m2 or 1m2
They are placed on the ground and the organisms within them are recorded
They can be used to measure the abundance of plants or slow-moving animals
Feeding relationships
Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers who are themselves eaten by tertiary consumers
Consumers that kill and eat other animals are predators, and those eaten are prey
a stable community the numbers of predators and prey rise and fall in cycles
The number of predators increases as there is more prey available
The number of prey then decreases as there are now more predators
The number of predators decreases as there is now less prey available
The number of prey increases as there are now fewer predators
The cycle now repeats
Pyramids of Biomass
We can measure the amount of biomass at different trophic levels in a food chain.
The total biomass of each trophic level is often represented as a modified bar chart called a pyramid of biomass.
In a food chain from a healthy ecosystem, the biomass at each trophic level must reduce.
Not all of the biomass is passed from the maize plants to the locusts
Biomass can be lost between stages because
not all of the matter eaten by an organism is digested
some of it is excreted as waste such as solid faeces, carbon dioxide and water in respiration and water and urea in urine.
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Required Practicals
Required practical - measuring population size in a habitat - Quadrat:
Aim:
To measure the species richness on the school field in areas in which the grass is regularly and irregularly cut.
Method:
choose a starting point on the school field in an area where the grass is often cut
use random numbers to generate a set of coordinates to place your first quadrat
count the number of different plant species within this quadrat (the species richness)
return to your starting position and repeat steps two and three a further 14 times using different random numbers
repeat steps one to four for a part of the school field which the grass is infrequently cut
compare your results by calculating a mean for each location
Quadrats can be used to measure abundance by recording:
The number of an individual species: the total number of individuals of a single species
Species richness: the total number of different species is recorded
Percentage cover: the approximate percentage of the quadrat area in which an individual species is found is recorded eg grass or moss.
Required practical - measuring population size in a habitat - Transect:
A transect is used to measure how the abundance of a species changes as you move along a changing habitat, eg. changing altitude on a hillside, or from open field to dense woodland, or along the shoreline at the coast
A line called a transect is set up through the changing habitat you want to investigate with a tape measure
A quadrat is then placed at regular intervals (eg. every 5 metres) along the transect
At each interval, the quadrat can be used to record the number of an individual species, species richness or percentage cover
Transects are useful for investigating how the abundance of a species is affected by an abiotic factor (e.g. light intensity, moisture levels, soil depth, altitude etc)
RP - effect of light or gravity on the growth of newly germinated seedlings
Method:
Put cotton wool into three petri dishes, and add the same volume of water to each dish.
Add ten seeds to each dish and place them in a warm place where they won’t be disturbed.
Allow the seeds to germinate, and add more water if the cotton wool dries out.
Once the seeds have germinated, ensure the petri dishes each contain the same number of seeds, and remove any extra seeds if necessary.
One petri dish will sit in full light on a windowsill, the second will be in a dark cupboard, and the final dish will be placed in partial light.
Every day for one week, measure the height of each seedling and record the results in a table. You must record the height of the individual seedlings on each day.
Calculate the mean of the seedlings each day, and compare the mean heights in the three different locations.
Investigate the effect of temperature on the rate of decay of fresh milk by measuring pH change:
Aim:
To investigate the effect of temperature on the rate of decay of fresh milk by measuring pH change.
Method:
Place 20 cm3 of fresh milk into three beakers
Decide the three temperatures you will investigate. Write these onto the sides of the beakers. They may be 5, 20 and 35°C.
Use universal indicator paper or solution to determine the pH of the milk in the three beakers
Cover each beaker in cling film and incubate at the appropriate temperature
Use universal indicator paper or solution to determine the pH of the milk in the three beakers after 24, 48 and 72 hours
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Genetic Engineering
Genetic engineering is changing the genetic material of an organism by removing or altering genes within that organism, or by inserting genes from another organism
The organism receiving the genetic material is said to be ‘genetically modified’. The DNA of the organism that now contains DNA from another organism.
- Plant genetic Engineering:
Genetically modified plants are plants that have had foreign DNA inserted into their genome
This is usually done to improve food production in some way For example:
Tomatoes have been genetically modified to make them grow larger fruit
Crop plants have been genetically modified to be resistant to diseases or resistant to certain herbicides
The gene for human insulin has been inserted
into bacteria which then produce human insulin which can be collected and purified for medical use to treat
people with diabetes.
The main steps in the process of genetic engineering:
Enzymes are used to isolate (cut out) the required gene
This gene is inserted into a vector
The vector is usually a bacterial plasmid (a piece of circular DNA found inside bacterial cells) or a virus
The vector is used to insert the gene into the required cells of the target organism
Genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics
Reflex arc
There are different types of neurones that work
together in a reflex action.
This creates an automatic and rapid response, which doesn’t involve the conscious part of the brain to a stimulus, which minimises any damage to the body from potentially harmful conditions, such as touching something hot.
Receptor in the skin detects a stimulus (the change in temperature).
Sensory neurone sends electrical impulses to relay neurone, which are located in the spinal cord. They connect sensory neurones to motor neurones.
Motor neurone sends electrical impulses to an effector.
Effector produces a response (muscle contracts to move hand away).
Synapse
Where two neurones meet there is a small gap,
a synapse.
An electrical impulse travels along the first axon.
This triggers the nerve-ending of a neurone to release chemical messengers called neurotransmitters.
These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the second neurone.
The receptor molecules on the second neurone bind only to the specific neurotransmitters released from the first neurone. This stimulates the second neurone to transmit the electrical impulse.
The Endocrine System
The human endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream
The blood carries the hormone around the body, and when it reaches a target cell/organ it produces an effect
Compared to the nervous system the effects of hormones are slower but they act for longer
Important structures in the endocrine system are:
Pituitary gland: a ‘master gland’ making hormones such as FSH and LH
Pancreas: produces insulin which regulates the blood glucose level
Thyroid: produces thyroxine which controls metabolic rate and affects growth
Adrenal glands: produces adrenaline
Ovaries (females): produce oestrogen
Testes (males): produce testosterone
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