Healthy Diet and Malnourishment
A healthy diet contains the right balance of the different foods you need and the right amount of energy.
These foods should provide the following nutrient groups:
- Carbohydrates for energy and to make cell structures
- Fat for energy, insulation and cell structures
- Protein to control cell reactions (as enzymes) and to build cell structures
- Vitamins and minerals to help our bodies function and regulate well.
Malnourishment may lead to a person being overweight or underweight- A person is malnourished if their diet is not balanced. An unbalanced diet may lead to diseases. Lack of essential nutrients in the diet can lead to deficiency diseases and excess intake of high energy foods can lead to type 2 diabetes.
- This is a disease where the person is unable to control the level of sugar in their blood.
- This is very dangerous, and the person must carefully control their diet and monitor their blood sugar levels regularly.
Exercise, Metabolic rate and Inheritance
Exercise increases the amount of energy expended by the body. People who exercise regularly are usually healthier than people who exercise less often. They expend more energy and their circulatory system becomes more efficient. They are likely to have lower blood pressure and less likely to be overweight.
Metabolic rate is the rate at which all the chemical reactions in the cells of the body are carried out. One major set of metabolic reactions is respiration, the rate of these reactions vary with the amount of activity you do. The more activity, the mre energy is required by the body. The metabolic rate also varies with respect to the proportion of muscle to fat in your body and the higher the proportion of muscle to fat, the higher the metabolic rate. Exercise increases the proportion of muscle to fat.
Inherited factors can influence our health- we can inherit genes from our parents which can influence our metabolic rate, we can also inherit genes which influence our cholesterol level. Cholesterol is a substance that our body creates fat that we consume in our diet- cholesterol is needed to make cell membranes. However, too much cholesterol can increase the chance of cardio-vascular diseases such as strokes and heart attacks.
Microorganisms and The immune system
Microorganisms that cause infectious disease are called pathogens.
Bacteria and viruses may reproduce rapidly inside the body and may produce poisons (toxins) that make us feel ill. Viruses damage the cells in which they reproduce.
The body has different ways of protecting itself against pathogens.
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.
The immune system of the body produces specific antibodies to kill a particular pathogen. This leads to immunity from that pathogen. In some cases, dead or inactivated pathogens stimulate antibody production. If a large proportion of the population is immune to a pathogen, the spread of the pathogen is very much reduced.
Semmelweiss and Antibiotics
Semmelweis recognised the importance of hand-washing 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 in his hospital.
Some medicines, including painkillers, help to relieve the symptoms of infectious disease, but do not kill the pathogens.
Antibiotics, including penicillin, are medicines that help to cure bacterial disease by killing infectious bacteria inside the body. Antibiotics cannot be used to kill viral pathogens, which live and reproduce inside cells. It is important that specific bacteria should be treated by specific antibiotics. The use of antibiotics has greatly reduced deaths from infectious bacterial diseases. Overuse and inappropriate use of antibiotics has increased the rate of development of antibiotic resistant strains of bacteria.
Many strains of bacteria, including MRSA, have developed resistance to antibiotics as a result of natural selection. To prevent further resistance arising it is important to avoid over-use of antibiotics.
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
- receptors in the ears that are sensitive to changes in position and enable us to keep our balance
- receptors on the tongue and in the nose that are sensitive to chemicals and enable us to taste and to smell
- receptors in the skin that are sensitive to touch, pressure, pain and to temperature changes
Simple Reflex Action
In a simple reflex action:
- impulses from a receptor pass along a sensory neurone to the central nervous system
- at a junction (synapse) between a sensory neurone and a relay neurone in the central nervous system, a chemical is released that causes an impulse to be sent along a relay neurone
- a chemical is then released at the synapse between a relay neurone and motor neurone in the central nervous system, causing impulses to be sent along a motor neurone to the organ (the effector) that brings about the response
- the effector is either a muscle or a gland, a muscle responds by contracting and a gland responds by releasing (secreting) chemical substances.
Hormones- Menstural Cycle
Many processes within the body are coordinated by chemical substances called hormones. Hormones are secreted by glands and are usually transported to their target organs by the bloodstream.
Hormones regulate the functions of many organs and cells. For example, the monthly release of an egg from a woman's ovaries and the changes in the thickness of the lining of her womb are controlled by hormones secreted by the pituitary gland and by the ovaries.
Several hormones are involved in the menstrual cycle of a woman. Hormones are involved in promoting the release of an egg:
- 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
- luteinising hormone (LH) stimulates the release of eggs from the ovary
- oestrogen is secreted by the ovaries and inhibits the further production of FSH
Control In Plants
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 (geotropism).
The responses of plant roots and shoots to light, gravity and moisture are the result of unequal distribution of hormones, causing unequal growth rates
Plant growth hormones are used in agriculture and horticulture as weed killers and as rooting hormones.
Scientists are continually developing new drugs.
When new medical drugs are devised, they have to be extensively tested and trialled before being used. Drugs are tested in a series of stages to find out if they are safe and effective.
Additional guidance - Candidates should understand that tissues and animals are used as models to predict how the drugs may behave in humans.
New drugs are extensively tested for toxicity, efficacy and dose:
- in the laboratory, using cells, tissues and live animals
- in clinical trials involving healthy volunteers and patients. Very low doses of the drug are given at the start of the clinical trial. If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug. In some double blind trials, some patients are given a placebo, which does not contain the drug. Neither the doctors nor the patients know who has received a placebo and who has received the drug until the trial is complete.
Thalidomide and Drugs In General
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 for use in pregnant women. Unfortunately, many babies born to mothers who took the drug were born with severe limb abnormalities. The drug was then banned. As a result, drug testing has become much more rigorous. More recently, thalidomide has been used successfully in the treatment of leprosy and other diseases.
Drugs change the chemical processes in peoples' bodies so that they may become dependent or addicted to the drug and suffer withdrawal symptoms without them. Heroin and cocaine are very addictive.
There are several types of drug that an athlete can use to enhance performance. Some of these drugs are banned by law and some are legally available on prescription, but all are prohibited by sporting regulations. Examples include stimulants that boost bodily functions such as heart rate; and anabolic steroids which stimulate muscle growth.
To survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there. Plants often compete with each other for light and space, and for water and nutrients from the soil whilst animals often compete with each other for food, mates and territory. Some organisms live in environments that are very extreme- Extremophiles may be tolerant to high levels of salt, high temperatures or high pressures.
Animals may be adapted for survival in dry and arctic environments by means of:
- changes to surface area
- thickness of insulating coat
- amount of body fat
Plants may be adapted to survive in dry environments by means of:
- changes to surface area, particularly of the leaves
- water-storage tissues
- extensive root systems.
Changes in the environment affect the distribution of living organisms- An example of this is the changing distribution of some bird species and the disappearance of pollinating insects, including bees.
Animals and plants are subjected to environmental changes. Such changes may be caused by living or non-living factors such as a change in a competitor, or in the average temperature or rainfall.
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 water.
Environmental changes can be measured using non-living indicators such as oxygen levels, temperature and rainfall.
Energy in biomass
Radiation from the Sun is the source of energy for most communities of living organisms. Green plants and algae absorb a small amount of the light that reaches them. The transfer from light energy to chemical energy occurs during photosynthesis. This energy is stored in the substances that make up the cells of the plants.
The mass of living material (biomass) at each stage in a food chain is less than it was at the previous stage. The biomass at each stage can be drawn to scale and shown as a pyramid of biomass.
The amounts of material and energy contained in the biomass of organisms is reduced at each successive stage in a food chain because:
- 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.
Waste materials from plants and animals and Decay
Many trees shed their leaves each year and most animals produce droppings at least once a day. All plants and animals eventually die. Microorganisms play an important part in decomposing this material so that it can be used again by plants. The same material is recycled over and over again and can lead to stable communities
Living things remove materials from the environment for growth and other processes. These 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 releases substances that plants need to grow.
In a stable community, the processes that remove materials are balanced by processes that return materials. The materials are constantly cycled.
The carbon cycle
In the carbon cycle:
- carbon dioxide is removed from the environment by green plants and algae for photosynthesis
- the carbon from the carbon dioxide is used to make carbohydrates, fats and proteins, which make up the body of plants and algae
- when green plants and algae respire, some of this carbon becomes carbon dioxide and is released into the atmosphere
- when green plants and algae are eaten by animals and these animals are eaten by other animals, some of the carbon becomes part of the fats and proteins that make up their bodies
- when animals respire some of this carbon becomes carbon dioxide and is released into the atmosphere
- when plants, algae and animals die, some animals and microorganisms feed on their bodies
- carbon is released into the atmosphere as carbon dioxide when these organisms respire
- The microorganisms and detritus feeders have broken down the waste products and dead bodies of organisms in ecosystems and cycled the materials as plant nutrients, all the energy originally absorbed by green plants and algae has been transferred
- combustion of wood and fossil fuels releases carbon dioxide into the atmosphere
Genetic variation and its control
There are not only differences between different species of plants and animals but also between individuals of the same species. These differences are due partly to the information in the cells they have inherited from their parents and partly to the different environments in which the individuals live and grow. Asexual reproduction can be used to produce individuals that are genetically identical to their parent. Scientists can now add, remove or change genes to produce the plants and animals they want.
Why organisms are different
The information that results in plants and animals having similar characteristics to their parents is carried by genes, which are passed on in the sex cells (gametes) from which the offspring develop.
The nucleus of a cell contains chromosomes. Chromosomes carry genes that control the characteristics of the body.
Different genes control the development of different characteristics of an organism.
Differences in the characteristics of different individuals of the same kind may be due to differences in:
- the genes they have inherited (genetic causes)
- the conditions in which they have developed (environmental causes)
- or a combination of both.
- Look at variation in leaf length or width, pod length, height. Compare plants growing in different conditions – sun/shade.
Reproduction and Genes
There are two forms of reproduction:
- sexual reproduction – the joining (fusion) 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.
Genes can also be transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with 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 genetically modified crops include ones that are resistant to insect attack or to herbicides
- genetically modified crops generally show increased yields.
Modern Cloning Techniques
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, eg a skin 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 to continue its development.
Particular genes or accidental changes in the genes of plants or animals may give them characteristics which enable them to survive better. Over time this may result in entirely new species. There are different theories of evolution.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
Other theories, including that of Lamarck, are based mainly on the idea that changes that occur in an organism during its lifetime can be inherited. We now know that in the vast majority of cases this type of inheritance cannot occur.
Studying the similarities and differences between organisms allows us to classify living organisms into animals, plants and microorganisms, and helps us to understand evolutionary and ecological relationships. Models allow us to suggest relationships between organisms.