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B1 - AQA GCSE Biology (from 2014)
Transcript of B1 - AQA GCSE Biology (from 2014)
We are made up of lot of cells and each of these cells carry out chemical reactions.
These reactions collectively are called our
How quickly these chemical reactions go on for is called our
Three main factors affect it:
The proportion of muscle to fat in your body
Microorganisms that cause diseases
This can be bacteria, viruses or fungi
Pathogens enter us through:
- The skin
- Consumption of food
- Being inhaled
- Openings such as the eyes
The body counters this by:
-Raising body temperature
-Producing tears which are slightly acidic
-Having an acidic stomach
-Cannot carry out any life processes
-Are much smaller than bacteria
-They inject themselves into a host cell
-They damage our cells internally
-It is debatable whether they are living or not
The Immune System
When pathogens enter the body, the body produces white blood cells.
There are two types of white blood cell
which engulf pathogens
which produce antibodies
-One celled microorganisms
-Can reproduce rapidly via cell division
These antibodies are produced to match the antigen on the pathogens.
Once this is done, white blood cells can be ingested and removed.
Decomposers need four things to break down material:
Glucose + Oxygen
Carbon Dioxide + Water (+Energy)
In order to release carbon they respire
These show the flow of food and energy from one organism to the next.
Energy is lost at every part of the food chain through:
Building plant compounds in plants
Building animal compounds in animal
Pyramids of Biomass
These show the biomass of organisms in a food chain.
In order to stay healthy, the human body requires a balanced diet.
This consists of:
If a person has an unbalanced diet, they are
This can lead to deficiency disease such as Type 2 Diabetes.
This is when a dead or inactive pathogen is injected into the body.
The body produces white blood cells to fight off the pathogens.
Once the body has produced the correct antibodies, it remembers the antigen so that next time, antibodies are produced more quickly to fight off the same pathogen, preventing illness.
To maximise yield, farmers reduce energy loss by:
- Reducing the length of the food chain
- Keeping animals in indoors so that less energy is used to regulate body temperature
- Keeping them in confined space so less energy is used for movement
These are used to treat painful symptoms from a disease. They
These are medicines that kill bacteria inside the body.
However, bacteria can develop a resistance to antibiotics.
When antibiotics are taken, most of the bacteria are killed.
However, one or two bacteria survive as they have mutated, making them resistant.
They pass this mutated gene onto their offspring, creating a new strain of antibiotic resistant bacteria.
MRSA: The importance of hygiene
MRSA is a very resistant strain of bacteria which causes skin infections.
However, it is easily killed with antiseptics and disinfectants which is why hospitals must practice good hygiene to prevent the spread of infection.
Before drugs are used to treat illness, they must be tested.
This is to make sure:
That they are
That the right
can be worked out
That there are
no side effects
- Originally developed as a sleeping pill
- Found to also cure morning sickness in pregnant women
- Had not been clinically trialled
- Caused birth defects
- Now used to treat leprosy
Clinical Drug Trials
1) Drugs are tested on cells and tissues
2) They are then tested on animals
3) They are tested on humans
Double blind trials
which are pills that do not contain the drug being tested.
Neither the patients or doctors know who is getting the placebo or the real drug which stops people from faking results, making the trial fair.
So what are drugs?
Drugs are chemicals that alter the body or brain
These are legal drugs which are allowed to be used but have a greater impact as they are more available.
Alcohol can harm the nervous system and alters peoples behaviour.
Nicotine can cause cancer and lead people to become addicted to tobacco.
Illegal recreational drugs
Athletes use steroids to develop their body, giving them an unfair advantage.
Drugs like cannabis are believed to have painkilling properties.
However, these can lead people onto harder drugs, like cocaine and heroin which are addictive.
Users often experience withdrawal symptoms.
Dwain Chambers was banned from the use of performance enhancing drugs.
which travel in the
The body uses hormones to control internal conditions in the body.
This is called
The body regulates four main things:
Our body has to be kept at
. This is so that enzymes in the body can work.
When we respire and exercise we produce heat. To cool us down we sweat.
We also loose heat when we breathe out warm air and through the warmth of our blood at the surface of our skin.
We need water otherwise chemical reactions do not go on in the body.
We lose water through sweating, breathing and through passing out urine.
A hormone produced by the brain also helps to regulate the kidneys to pass out excess water.
Glucose is carried in the blood stream to cells for respiration.
Hormones regulate this to ensure that there is never too much or too little glucose in the blood.
These ensure that various body fluids are at the right pH and our nerves working.
Hormones work with the kidneys to pass out unwanted ions to keep our ionic content balanced.
The Menstrual cycle
Hormones are also used in the menstrual cycle.
There are three main ones:
- Secreted from the pituitary gland
- Secreted in the ovaries
- Inhibits (stops) the production of FSH
- Stimulates lining of the uterus
- Stimulates the release of LH
- Secreted from the pituitary gland
- Stimulates ovulation from the ovaries
The Contraceptive Pill
Oestrogen inhibits FSH so it can be used in pills to prevent eggs maturing and ovulation.
- Stimulates eggs to mature in the ovaries
- Also stimulates the production of oestrogen in the ovaries.
Controlling Fertility: IVF
This is used when a female has difficulty trying to conceive.
1) Doctors give the woman FSH and LH which produces many eggs
2) These eggs are then harvested from the mothers uterus and mixed with the fathers sperm in a dish
3) The eggs and the sperm fertilise and embryos start to develop
4) A few embryos are then selected and placed back inside the mothers uterus.
Ethical issues of IVF
- Not all embryos are allowed to develop into people
- Some think infertile couples should adopt instead
- Those that are infertile are able to have children
- Genetic disorders can be tested for being implanted
Hormones in plants
Hormones are also used in plant growth
Auxin is used in weedkillers and also in rooting powders so that cuttings produce new roots.
Auxin is a hormone which also responds to
changes in stimuli.
Changes in stimuli
All living things respond to changes in the environment. These changes are called
In plants, a response to a stimulus is called a tropism.
This is where plants respond to gravity.
Roots grow downwards as a result as the auxin is unevenly distributed along the tips of the root.
There are two parts to the nervous system:
The central nervous system (CNS) which is the brain and spinal cord.
The peripheral nervous system which are nerves taking information to and from the CNS.
Humans also respond to stimuli and we detect these through receptors and sense organs that are a part of our central nervous system.
These are involuntary responses which are not controlled by the brain.
These responses follow a certain path way in the body.
Between neurones there are gaps called
Electrical impulses cannot travel along these gaps so once they reach a nerve ending they are converted into a
These chemicals diffuse across the synapse onto the next neurone where it is converted back into an electrical impulse.
Adapting to change
Many animals have adaptations to help them survive in harsh environments.
These are features of an animals body which help it to live in its environment.
Have small ears - Reduced surface area so heat loss is reduced
Thick white hollow fur - Insulates the body and reduces heat loss by trapping air and used to camouflage from prey
Blubber underneath the skin - Used to store fat that can be used for respiration to generate heat
Has large ears - Bigger surface area so more heat loss.
Large Surface Area to Volume ratio - More heat loss.
Thick fur - Insulation so the animal can keep warm at night
Lives in burrows to reduce water loss and keep cool during the day.
Plants also have adaptations too
Wax on the stem - reduces water loss
Spines as leaves - reduces surface area and water loss
Swollen stem - stores water
Shallow widespread roots in order to collect water from underground and when it rains
Competition for resources
All living things compete for resources
Plants compete for:
Animals compete for
Changes in distribution
The number of organisms of a species in an area is called a
If there is a variety of species in this area then it is
Organisms can move habitat due to factors such as:
Lack of food
Pollutants can harm organisms in the environment and can be monitored in two ways:
(Species that are only present in certain levels of pollution)
(Temperature, pH, oxygen level)
Lichens change colour if there is pollution present.
Red tailed maggots are animals that can live in areas with a
high biological demand (BOD)
This means that they live in areas where there is very little oxygen
Plants take in CO2 for photosynthesis in order to build molecules.
They also respire, releasing CO2 back into the atmosphere.
Animals eat plant material taking in carbon locked into these molecules.
Animals release this through respiration in the form of CO2
Carbon locked up in dead plants and animals turns into fossils over millions of years.
These fossil fuels are then burnt in combustion releasing CO2 back into the atmosphere
The Carbon Cycle
Within a species there is variation.
These variations can be determined by the environment or by our
Our genetic information is contained the
Inside the nucleus there are structures called
Chromosomes are found in pairs containing genetic information.
Half of the genes are from one parent and the other half of the genes are from the other.
Genes have coded information which determines certain characteristics
There are two types of reproduction:
This involves two different sex cells joining which are called
Each gamete has
the number of chromosomes of a normal body cell
The female gamete is called an egg and the male gamete is called a sperm
When these two cells fuse together, the nuclei from both cells fuse together and the chromosomes pair up creating a full set.
This form of reproduction results in
- Only requires one parent
- No gametes are involved
- No mixing of genetic information
Results in offspring which are
to each other and the parent
This is where parts of a plant are taken and regrown.
The advantages of this are that it is a
to grow plants
from the parent plant are also kept in the offspring
Adult cell cloning
This is where plant cells or tissue is extracted from a plant
It is then placed in a special liquid jelly with nutrients to help the plant grow
This method is often used in producing cattle with desirable characteristics
Eggs are taken from the female cows with the desired characteristics
Sperm is also taken from the bull
The eggs and the sperm fertilize in a dish and are left to develop into embryos
Once the embryos have developed they are placed into the womb of a
Dolly the Sheep
1) A body cell is taken from Sheep A and the nucleus is extracted and kept.
This is because it has a FULL set of chromosomes
2) An egg cell is extracted from Sheep B and the nucleus is extracted but destroyed
3) The nucleus from Sheep A and the remaining egg from Sheep B are then fused together giving the egg cell a full set of chromosomes
4) The egg cell is given an electric shock which stimulates embryo growth
5) The developed embryo is then placed into the uterus of a surrogate sheep (Sheep C)
This is the process of changing an organisms genes.
This method is used often to make insulin using bacteria
1) The gene for insulin is found and extracted using enzymes .
2) A bacteria's plasmid is extracted and enzymes cut hole for the insulin gene.
3) The gene is placed into the plasmid and this is put back into the bacteria
4) The bacteria are left to multiply making insulin in the process which is extracted
Genetically Modified (GM) Foods
Genetically modifying crops can be advantageous because:
- Crops can survive in harsh conditions
- They can made resistant to pests and weed killer
- They can contain nutrients that would not normally be found
- They can be made to look more appealing
Concerns about GM crops
- GM crops do not always have a high yield.
- Protesters believe it is interfering with nature
- They can be used to solve food shortages
- They can be more nutritious than normal crops
- Less pesticides can be produced
There are often similarities and differences between organisms so they are put into groups
If two species are closely related they have more characteristics. This is because the had a common ancestor
An example of a biological family tree
1) There is variation within a population due to mutations in genes
2) The ones with an advantageous gene or trait are able to survive better.
3) The ones without the advantageous gene die out leaving a dominant species
4) The dominant species pass this gene onto their offspring
Evidence for Darwin's theory
- Fossilised evidence
- Variety between finches on the Galapagos Islands
Why it was not accepted at the time
- His ideas went against the religious viewpoint of creationism
- Scientists did not know about genes, so could not explain how characteristics were passed on
Another scientist called Jean Lamarck said that animals evolved based on using a characteristic repetitively before passing this new characteristic onto their offspring
This theory is not accepted because only genetic information is passed onto offspring.
This is a waxy substance in the body which helps strengthen cell membranes and helps produce vitamin D.
However, too much can increase the risk of heart disease.
These are enzymes that inhibit the enzymes involved in making cholesterol.
This is often used for people which produce too much cholesterol due to genetics.