Biology

A healthy diet contains the right balance of the different foods you need and the right amount of energy.

Carbohydrates - to release energy 

Fats - to keep warm and release energy 

Proteins - to build cells 

Fibre - to keep everything running smoothly in the digestive system 

Mineral ions and vitamins - needed in small amounts for the healthy functioning of the body.

A person is malnourished if their diet is not balanced. This may lead to a person being overweight or underweight. An unbalanced diet may also lead to deficiency diseases or conditions such as Type 2 diabetes. 

People who exercise regularly are usually healthier. 

People  who exercise are less likely to suffer from healthy problems such as obesity. 

A person loses mass when the energy content of the food taken in is less than the amount of energy used  by the body. Exercise increases the amount of energy used by the body.

Exercise builds muscles so it helps to boost your metabolic rate.

Metabolic rate - The rate at which all the chemical reactions in the cells of the body are carried out.

The metabolic rate varies with the amount of activity you do and the proportion of muscle to fat in your body.

Metabolic rate may be affected by inherited factors.

Inherited factors also affect out health; for example, cholestrol level.

Cholesterol is a fatty substance that's essential for good health. Some inherited factors increase blood cholesterol level, which increases the risk of heart disease.

Pathogens - Microorganisms that cause infectious diseases

Bacteria and viruses may reproduce rapidly inside the body and may produce toxins that make us ill. Viruses damage the cells in which they reproduce.

White blood cells help to defend against pathogens by:

• ingesting pathogens 
• producing antibodies, which destroy particular bacteria or viruses 
• producing antitoxins, which counteract the toxins released by the pathogens

Semmelweis recognised the importance of handwashing in the prevention of spreading some infectious diseases. By insisting that doctors washed their hands before examining patients, he greatly reduced the number of deaths from infectious diseases. 

The immune system produces specific antibodies to kill a particular pathogen. This leads to immunity from that pathogen. 

Vaccinations involve injecting small amounts of dead or inactive pathogens/antigens which cause your body to produce antibodies to attack them. 

If live pathogens enter your body, the white blood cells can quickly identify them and rapidly produce antibodies to kill the pathogen. 

Some medicines, including painkillers, help relieve the symptoms of an infectious disease but do not kill the pathogen.

Antibiotics - medicine that help to cure bacterial disease by killing infectious bacteria inside the body.

• Antibiotics cannot be used to kill viruses because they do not work inside cells.
• Overuse and inappropriate use of antibiotics have increased the rate of development of antibiotic resistant strains of bacteria.
• MRSA, have developed resistance to antibiotics as a result of natural selection. 

Mutations of pathogens produce new strains. Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen.

The nervous system enables humans to react to their surroundings and coordinate their behaviour 

Cells called receptors detect stimuli (changes in the environment)

Receptors and the stimuli they detect include:

• receptors in the eyes that are sensitive to light
• receptors in the ears that are sensitive to sound and changes in position 
• receptors on our tongue and in the nose that are sensitive to chemicals
• receptors in the skin that are sensitive to touch, pressure, pain and temperature changes

Light receptors cells have a nucleus, cytoplasm and cell membrane.

Information from receptors passes along cells (neurones) in nerves to the brain. The brain coordinates the response. Reflex actions are automatic and rapid. They often involve sensory, relay and motor neurones.

Central nervous system consists of the brain and spinal cord 

In a simple reflex action:

• Impulses from a receptor pass along a sensory neurone to the CNS
• At a junction (synapse) between a sensory and relay neurone, a chemical is released that causes the impulse to be sent along a relay neurone.
• A chemical is then released at the synapse between the relay and motor neurone, causing impulses to be sent along a motor neurone to the organ (the effector) 
• The effector is either a muscle or gland, a muscle responds by contracting and a gland responds by releasing chemical substances.

Internal conditions that are controlled include:

• the water content  - water leaves the body via lungs when we breathe out and via the skin when we sweat to cool us down and excess water is lost via the kidneys in the urine
• ion content - ions are lost via the skin when we sweat and excess ions are lost via the kidneys in the urine
• temperature - to maintain the temperature at which enzymes work best 
• blood sugar levels - to provide the cells with a constant supply of energy. 

Hormones regulate the functions of many organs and cells. 

Hormones are secreted by the glands and are transported by the bloodstream.

Hormones are involved in the menstrual cycle of a woman:

• follicle stimulating hormone (FSH) is secreted by the pituitary gland and causes eggs to mature in the ovaries. It also stimulates the ovaries to produce hormones including oestrogen.
• LH stimulates the release of eggs from the ovary. 
• Oestrogen is secreted by the ovaries and prevent the further production of FSH.

The use of hormones in controlling fertility include:

• giving oral contraceptives that contain hormones to prevent FSH production.
• oral contraceptives may contain oestrogen and progesterone to prevent egg maturation 
• giving FSH and LH in a fertility drug to a woman to stimulate eggs to mature

The first birth control pill contained large amounts of oestrogen. These resulted in women suffering significant side effects. Birth control pills now contain a lower dose of oestrogen or are progesterone only.

Plants are sensitive to light, moisture and gravity:

• their shoots grow towards light and against the force of gravity 
• their roots grow towards moisture and in the direction of the force of gravity 

Plants produce hormones to coordinate and control growth. Auxin controls phototropism and gravitropism 

Plant growth hormones are used in agriculture and horticulture as weed killers and as rooting hormones.

When medical drugs are created they have to be tested and trialled before being used.

New drugs are tested for toxicity, efficacy and dose:

• in the laboratory, using cells, tissues and live animals
• in clinical trials involving healthy volunteers and patients. The drug is given in small doses. If the drug is found to be safe, further clinical trials are carried out to find the optimum dose.
• in some double-blind trials, some patients are given a placebo, which does not contain the drug. Neither the doctor nor the patients know who has received a placebo.

Thalidomide is a drug that was developed as a sleeping pill. It was also found to be effective in relieving morning sickness in pregnant women.

Thalidomide had not been tested on pregnant women. Unfortunately, many babies born to mothers who took the drug were born with severe limb abnormalities. 

As a result drug testing has become more rigorous.

Thalidomide had been used successfully in the treatment of leprosy and other diseases.

Cannabis is an illegal drug. Cannabis smoke contains chemicals which may cause mental illnesses in some people.

The overall impact of legal drugs on health is much greater than the impact of illegal drugs because far more people use them.

Drugs change the chemical processes in people's bodies so that they may become dependent or addicted to the drug and suffer withdrawal symptoms without them. 

Some athletes take performance-enhancing drugs to make them better at sports. Examples include stimulants that boost bodily functions such as heart rate; and anabolic steroids which stimulate muscle growth. These drugs can have negative health effects.

Desert animals have adapted to save water and keep cool.

• Large surface area compared to volume
  • This lets desert animals lose more body heat, which helps them stop overheating 
• Efficient with water
  • Desert animals lose less water by producing small amount of concentrated urine
  • They also make very little sweat. Camels are able to do this by tolerating big changes in body temperatures.
• Good in hot conditions 
  • Desert animals have very thin layers of body fat and a thin coat to help them lose body heat. E.g. camels keep nearly all their fat in their humps 
• Camouflage 
  • A sandy colour gives good camouflage - to help them avoid predators, or sneak up on prey 

Arctic animals have adapted to reduce heat loss

• Small surface area compared to volume 
  • Animals living in cold conditions have a compact shape to keep their surface area to a minimum - this reduces heat loss
• Well insulated 
  • They also have a thick layer of blubber for insulation - this also acts as an energy store when food is scarce.
  • Thick hairy coats keep body heat in and greasy fur shed water (this prevents cooling due to evaporation)
• Camouflage 
  • Arctic animals have white fur to help them avoid predators, or sneak up on prey 

Desert plants have adapted to have little water.

• Small surface area compared to volume
  • Plants lose water vapour from the surface of their leaves. Cacti have spines instead of leaves - to reduce water loss
  • They also have a small surface area compared to their size which also reduces water loss
• Water storage tissues 
  • For example, cactus stores water in its thick stem 
• Maximising water absorption 
  • Some cacti have shallow but extensive roots to absorb water quickly over a large area. Other have deep roots to access underground water.

Extreme Adaptations

Some microorganisms (e.g. bacteria) are known as extremophiles - they're adapted to live in seriously extreme conditions like super-hot volcanic vents, in salty lakes or at high pressure on the sea bed.

Organisms need things from their environment and from other organisms in order to survive and reproduce.

• Plants need light, space, water, and minerals (nutrients) from the soil.
• Animals need space, food, water and mates 

Environmental changes are caused by living factors and non-living factors such as:

• A change in the occurrence of infectious diseases 
• A change in the number or predators 
• A change in the number of prey or the availability of food 
• A change in the number of competitors
• A change in temperature 
• A change in average rainfall
• A change in the level of air or water pollution.

Changes in the environment affect the distribution of living organisms

Living organisms can be used as indicators of pollution 

• Lichens can be used as air pollution indicators, particularly of the concentration of sulfur dioxide in the atmosphere
• Invertebrate animals can be used as water pollution indicators and are used as indicators of the concentration of dissolved oxygen in the water.

Environmental changes can be measured using non-living indicators such as oxygen levels, temperature and rainfall.

• Satellites to measure the temperature of the seas surface and the amount of snow and ice cover
• Automatic weather stations tell us the atmospheric temperature
• Rain gauges measure rainfall 

Radiation from the sun is the source of energy fro most living organisms. 

The mass of living material (biomass) at each stage in a food chain is less than it was the previous stage. The biomass at each stage can be shown as a pyramid of biomass

• Some materials and energy are always lost in the organisms' waste materials.
• Respiration supplies all the energy needs for living processes including movement. Much of this energy is eventually transferred to the surroundings.

Many trees shed their leaves each year and most animals produce droppings. All plants and animals eventually die. 

Living things remove materials from the environment for growth and other processes. The materials are returned to the environment either in waste materials or when living things die and decay 

Materials decay because they are broken down (digested) by microorganisms. Microorganisms are more active and digest materials faster in warm, moist, aerobic conditions.

The decay process release substances that plants need to grow.

Most cells in you body have a nucleus. The nucleus contains your genetic material in the form of chromosomes 

The human cell nucleus contains 23 pairs of chromosomes. 

Chromosomes carry genes. Different genes control the development of different characteristics.

The DNA is coiled up to from the arms of the chromosomes. 

Sexual reproduction - the joining of male and female gametes. The mixture of the genetic information from two parents leads to variety in the offspring.

Asexual reproduction - no fusion of gametes and only one individual is needed as the parent. There is no mixing of genetic information and so no genetic variation in the offspring. These genetically identical individuals are known as clones.

New plants can be produced quickly and cheaply by taking cuttings from older plants. These new plants are genetically identical to the parent plant.

Modern cloning techniques include:

• Tissue culture - using small groups of cells from part of a plant 
• Embryo transplants - splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers.
• Adult cell cloning - the nucleus is removed from an unfertilised egg cell. The nucleus from an adult body cell is then inserted into the egg cell. An electric shock then causes the egg cell to begin to divide to form embryo cells. These embryo cells contain the same genetic information as the adult skin cell. When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female.

In genetic engineering, genes from the chromosomes of humans and other organisms can be cut out using enzymes and transferred to cells of other organisms.

Genes can be transferred to the cells of animals, plants or microorganisms so that they have desired characteristics.

• New genes can be transferred to crop plants 
• Crops that have had their genes modified in this way are called genetically modified crops (GM crops)
• Examples of GM crops include ones that are resistant to insert attack or to herbicides
• GM crops generally show increasing yields.

Concerns about GM crops include the effect on populations of wildflowers and insects, the uncertainty about the effects of eating GM crops on human health

Darwin's theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.

The theory of evolution by natural selection was only gradually accepted because:

• The theory challenged the idea that God made all the animals and plants that live on Earth.
• There was insufficient evidence at the time the theory was published to convince many scientists 
• The idea of inheritance and variation was not known until 50 years after the theory was published.

Lamark's theory states that changes that occur in an organism during its lifetime can be inherited. 

Evolution occurs via natural selection:

• Individual organisms within a particular species may show a wide range of variation because of differences in their genes
• Individuals with characteristics most suited to the environment are more likely to survive to breed successfully 
• The genes that have enabled these individuals to survive are then passed on to the next generation.

Studying the similarities and differences between organisms allows us to classify living organisms into animals, plants and microorganisms.