support and movement

When plant cells take up lots of water by osmosis they become rigid, like a blown up balloon. We say they are turgid. This provides a lot of support to plants. When a plant dries out the cells lose their turgidity, which is why the leaves start to wilt.


Most of the largest plants we see, such as trees, have wood in them. Wood provides a lot of support and prevents branches from breaking or from wilting if they dry out. Lignin is the substance produced in the cells of woody plants that gives them this structure.

The skeleton of a mammal is made of bone and cartilage. Bone is a lot stronger than cartilage, because it needs to provide support for the body and a firm structure for muscles to attach to so that they can move parts of the body. Cartilage is the softer substance found in your ears, in your nose and between the joints. Cartilage does not contain as much calcium as bone, so it is more flexible which is why you can bend your ears. It is also smoother, which is why it is found in joints to stop the bones from rubbing together.

You need to know the names and positions of the following parts of the arm: the ulna, radius, humerus, scapula, tendons, biceps an triceps. The two bones in the forearm are the radius and the ulna. The ulna is the one that forms the elbow. The humerus is the bone in the upper arm. The scapulas are also known as the shoulder blades and are the plates located on your upper back. The biceps and the triceps are found either side of the humerus. When the biceps contracts it pulls on the bones in the forearm and bends the arm. When the triceps contracts it pulls on the part of the ulna that sticks out to make the elbow and this straightens the arm.

The contraction of these muscles produces a turning effect, with the elbow acting as the pivot. You may remember from your physics that the ?moment? (or turning force) is the force multiplied by its perpendicular distance (distance at right angles) from the pivot. This means that there is a bigger moment if the force is not acting near the pivot. This is why door handles are not near the hinge. The design of the human arm has the muscles attached very close to the pivot. Therefore they need to produce very large forces in order to move the arm. The arm could lift much heavier weights if the muscle was attached near the hand, but of course it would get in the way. You might be asked to make some moments calculations to do with the arm.

A joint occurs wherever two bones meet. Not all joints can move (for instance the various bones in your skull are fixed in place). A synovial joint allows the movement of two bones without the bones rubbing together and causing damage. The bones have a layer of cartilage at the ends and synovial fluid in the gap between the bones helps reduce friction, a bit like oil in a motor.

Organisms in their Environment

A population is all the individuals of a particular species that live in one area. For instance, you can have the population of fleas on a dog, or the population of fleas in El Salvador. If the conditions are perfect a population will grow. Eventually the population will get so big that there is not enough food, or not enough space, or too much disease, or too many predators, or some other factor that limits the population size, so the population stops growing.

We can draw graphs of population size against time which often have characteristic shapes. When nothing in the environment limits the growth of the population we see an exponential curve. This is where the graph gets steeper and steeper and steeper. This is what has happened to human populations throughout history. We have not yet reached our limit (though we will soon), but usually the graph stops getting steeper and flattens out, giving a characteristic sigmoid shape (sigmoid is like a flattened S shape).

In any habitat there will be many different populations that all have an effect on each other. This is called the community. The habitat will also affect the community because of such things as temperature, amount of water etc. The community and habitat together are known as the ecosystem.

An ecosystem gets all of its energy from sunlight. Plants absorb sunlight during photosynthesis and use it to produce complex chemicals such as glucose and proteins. An animal cannot make these chemicals, so to get them it needs to consume plants, or other animals that have consumed plants. When these animals and plants die the energy they contain is not wasted. Other organisms such as bacteria and worms feed on the decomposing remains of dead organisms. In this way, energy passes along a food chain from sunlight to plants (which we call producers), to animals (which we call consumers) to decomposers.

At the end of the food chain very little of the original energy from the sunlight remains for the decomposers. This is because much of the energy has been used up by the plants and animals further down the chain (of course remembering that we cannot create or destroy energy, only transfer it from one form into another ? in this case the organisms have transferred it mostly into heat energy). This is why the animals at the top of the food chain (the tertiary consumers), such as eagles, jaguars, wolves etc are generally quite rare, whereas plants and primary consumers (the animals that eat plants) are much more common.

We can represent the number or organisms in a food chain by using a pyramid of numbers. We call it a pyramid because usually there are less individuals the further up the food chain that you go. However this is not always the case. For example you can have thousands of insects living on one tree because the tree is so big. In this case it is better to use a pyramid of biomass (the dry mass of the organisms at each step in the food chain). This is because even though there are more insects than trees, there is a far greater mass of tree than there is of insects.

The pyramid of numbers can also tell us something about how humans can get more food from the land. If energy is lost on its way up the food chain then humans will get more energy out of their land if they grow crops than if they raise animals. An area of land may grow enough lettuces to feed one hundred people, but if you feed the lettuces to rabbits and then eat the rabbits you may only feed about 10 people, because typically only about 10% of the energy is passed from one level in the food chain to the next. Occasionally, it will still be important to eat some animals because they provide an important source of protein which only certain plants can provide.

Inheritance

The individuals of any species are never exactly the same. This is partly because they have different genes and partly because they have had different experiences in their lives or lived in different environments. For example, a single gene determines the colour of a persons eyes and the environment has no effect. In contrast, any scars a person has are only the result of the environment. Some things are a mixture of both; for instance a tall person may have genes that help make them tall, but they also need to eat the correct food to help them grow.

The difference between continuous and discontinuous variation often confuses people. Continuous variation means that a characteristic can be almost anything between two extremes. For example, some people are very tall and some people are very short. These are the extremes. Other people can be ANY size in between. On the other hand, discontinuous variation means that there are only specific categories that you can belong to. An example is blood group. A person is either A, B, AB, or O and can be either positive or negative. You cannot be half way between the two, you are either completely one or completely another.

The nucleus in cells contains a chemical called DNA. This is found in long strands called chromosomes. Humans have 46 chromosomes, whilst other organisms have more, less or even the same number as us. The DNA contains sets of coded instructions for making proteins. These proteins will help determine the characteristics of an organism. A set of coded instructions to make a protein is called a gene. Humans have about 100,000 different kinds of gene (we actually have up to two versions of each gene). Almost all of the cells in a person?s body will have exactly the same 46 chromosomes containing the same 100,000 genes. Eye colour is controlled by a single gene, because the colour is caused by a single protein. Some more complicated features, such as the brain, require many proteins so are controlled by many genes.

The only cells that are different are the red blood cells, because they don?t have a nucleus so don?t have any DNA, and the sex cells (sperm and eggs). Each sperm cell only contains half of a man?s chromosomes (23). Equally, each egg contains only half of a woman?s chromosomes. This is important because it means that when an egg and a sperm join together during fertilization, the new zygote that forms will have the correct number of 46 chromosomes; half of which were obtained from each parent.
Earlier I mentioned that we have up to two copies of each gene. One copy of each of the 100,000 genes we received from our father and the other copy of each of the 100,000 genes we received from our mother. This means that we might receive a different version of a gene from each parent. The different versions of a gene are called the alleles. There is a singe gene that controls our eye colour. However, there are several different alleles that we can have, ie blue, brown, green etc. We might get, say, a brown allele from one parent and a blue allele from the other parent. Eye colour has discontinuous variation, so we can only be one colour or the other ? we cannot be a mixture of the two. What happens is that one allele is DOMINANT to the other allele, which we call RECESSIVE. In humans, the brown eye colour allele is always dominant to the blue eye colour allele. In this case the child would have brown eyes, even though they also carry the allele for blue eyes. In this case we say they are HETEROZYGOUS, because the two alleles for that gene are different. A person who receives the allele for blue eyes from both parents will have blue eyes. Both of the alleles are the same, so we say they are HOMOZYGOUS. A good way to remember which is which is to remember that a homosexual fancies people from the same sex and a heterosexual fancies people from a different sex. We can see from this that by looking at the type of features a person has (their PHENOTYPE) we can not necessarily tell what type of genes a person has (their GENOTYPE).

Geneticists are able to predict what genotypes and phenotypes will occur in the offspring when two organisms are bred together. Any mating of this kind we call a genetic cross. It can be represented using a punnett square. For example, in pea plants, tall plants are dominant to short plants. In this case tall is dominant so we will use the letter T to represent tall and t to represent short (this is the standard way of writing it using the capital letter of the first word to describe the dominant allele and the same letter in lower case to represent the recessive allele ? we do not use T and S). If the male plant had the genotype Tt and the female plant had the genotype tt, then the possible pollen that can be made by the male are T or t. When the female plant produces ovules it will produce only t and t.

We can use a punnett square as follows to show the proportions of each genotype and phenotype that we would expect to find in the offspring.






We can see from this cross that half of the genotypes are heterozygous Tt. The T is dominant to the t, so we can say that half of the offspring will have tall phenotypes. Half of the genotypes are homozygous tt. In this case the recessive characteristic will result in a short phenotype. The ratio of tall plants to short plants in this case would be 1:1.

You need to be able to conduct crosses like this using a punnett square and be able to work out the expected ratios of the different genotypes and phenotypes. Remember that they are only ?expected? ratios. If we actually did the cross shown above with real pea plants and had 1000 offspring, we would expect about 500 to be tall and 500 to be short. However, it would not always be exact because it depends which pollen grain fertilizes which ovule so you could easily find that the numbers are a little bit out, say 485 tall and 515 short.

Sometimes a piece of DNA can be mutated. This means that it becomes slightly changed. Sometimes this occurs naturally, but it is especially common wherever there is radiation, because radioactive particles moving at incredibly high speeds can collide with the complicated DNA structure and alter it. Usually, if a normal body cell is mutated in this way it does not cause too many problems. The exception is when it causes the cell to start dividing uncontrollably into a ball of cells called a tumor. This is called cancer. Another problem is caused when the DNA of a sex cell is damaged. This is worse because the damage is passed on from one generation to the next. We call this a genetic disease.

Sickle-cell anaemia is a genetic disease that affects the red blood cells. When the oxygen levels are low the cells form into a sickle shape and can block the capillaries causing pain and in severe cases severe damage or even death. You might then ask the question ?if its so harmful, why hasn?t sickle cell anaemia disappeared through evolution?? The answer is that it can also be an advantage to have the sickle cell allele. People who are heterozygous do not suffer much from the disease, but they have the advantage that they are immune to Malaria, because the parasite cannot live in their blood. This is why in most parts of the world the sickle cell allele is very rare, but in areas with lots of malaria it is very common.

Genetic engineering is a relatively new method whereby scientists are able to take a gene from one organism and put it into another. One famous example is where the gene to make human insulin was removed from a human cell and inserted into a bacteria cell. These bacteri now make human insulin for diabetics to use. Many crop plants and farm animals can also be altered in this way. There can be problems if mistakes are made which cause harmful results that were not expected.

Modern cloning techniques allow the production of plants with identical genes. This has benefits for agriculture, because farmers know exactly how to look after their crop because there is no variation between the individual plants.

Reproduction in human

You need to know the structure of the female reproductive organs (see the handouts you were given in class) and also the functions of the main parts.

Adolescence (puberty) is controlled by the sex hormones. The male sex hormone is called testosterone and it is produced in the testes. The female sex hormones are called oestrogen and progesterone and they are produced in the ovaries.

Male
Sperm is produced in the testes. A liquid is produced in the seminal vesicles and prostate gland and mixed with the sperm to form semen, which is stored in the seminal vesicles. The man?s penis is made of spongy tissue that fills up with blood when the man is sexually aroused. This makes the penis become erect. During intercourse the penis is inserted in to the woman?s vagina. Stimulation of the penis causes an ejaculation, where the semen is squirted from the seminal vesicles through the urethra (tube in the penis) into the woman?s vagina. The sperm then swim up into the vagina and then into the oviducts to fertilise an egg, if one is present.

Female
An egg is produced every month in one of the ovaries. It passes down the oviduct (or fallopian tube) and then into the uterus (womb). It then goes through the cervix (the part separating the uterus from the vagina) and then passes out through the vagina. However, if the woman has had sexual intercourse there are sperm in the oviducts. Fertilisation takes place when the sperm and the egg fuse to form a zygote.

The menstrual cycle
In the weeks leading up to ovulation (the release of an egg) an egg develops in one of the ovaries and the uterus develops a thick lining with lots of blood vessels. If an egg is fertilized it will fix itself to this lining and develop into an embryo. The blood supply will provide it with nutrients until the placenta grows. If an egg is not fertilized this thick lining is no longer needed and is passed out through the vagina. This is known as menstruation or the period.

The embryo develops in the uterus and grows into a fetus. It receives nutrients and oxygen from the mother via the placenta. It also gets rid of waste (such as CO2) this way. The mother?s and baby?s blood does not mix in the placenta, but they do pass very close to each other so that these substances can be transferred between them. The fetus develops inside a sac called the amnion that is filled with a liquid called the amniotic fluid. This provides protection for the baby. One of the first signs that a woman is about to give birth is when this sac breaks and the liquid inside passes out of the vagina. Muscular contractions in the uterus build up over the next hour or more until they become so strong that the baby is forced out of the uterus through the vagina. The umbilical cord that attaches the baby to the placenta is cut. The baby no longer receives oxygen from the mother so it needs to start breathing. The placenta is ejected from the uterus shortly after the baby (its often called the afterbirth).

There are more people born in the world each year than there are people who die. This means that the human population is rising rapidly. This is causing many problems, because in some countries there is not enough food or space for everyone. One solution is for people to use some form of birth control (such as contraceptives) to limit the number of children being born.

AIDS is a serious disease that is spreading rapidly throughout the world, especially in some areas such as Africa. AIDS is caused by the HIV virus. The virus is found in the body fluids (such as blood, semen, vaginal secretions etc). Anything that results in the fluids of an infected person entering a healthy person can result in transmission (the virus being passed from person to person). The most common ways of transmission are from sexual intercourse, the sharing of needles by doctors and drug addicts and through blood transfusions (though nowadays the blood is usually tested first). The use of condoms during sexual intercourse and the use of clean needles would help to limit the spread of AIDS.

Reproduction

There are two types of reproduction:
Asexual reproduction
Asexual reproduction produces offspring that are identical to the one parent. One example is the splitting of bacteria into two. Another is when gardeners make cuttings, by removing a small piece from a plant and placing them in the ground to grow into a new plant.

Sexual reproduction
Sexual reproduction involves two parents mixing their genes to produce offspring that are genetically different from them. This is carried out by a mobile gamete, (which contains half of the males genes), such as a sperm or a pollen grain, fusing with a stationary female gamete (containing half of the female?s genes), such as an egg or an ovule.

The fusion of the male and female gametes is called fertilization. Some species (eg fish) use external fertilization. In this case millions of eggs and sperm are released into the water and fertilization takes place in the open water. Usually the adults do not care for the young so the survival rate is low. This is why so many gametes are needed. Some species (eg humans) use internal fertilization, which means that fertilization takes place inside the woman?s body (the fallopian, or egg tubes). This means that less sperm is wasted and also means that the young can grow safely inside the woman?s body. Animals on land cannot use external fertilization, because the sperm needs to be able to swim to the egg.

Insect pollinated flowers (you need to know the structure) produce sweet nectar that the insects feed on. They have brightly coloured petals and smells to attract the insects. The pollen is found on the anther, which is situated at the end of a long filament. When an insect visits the flower the pollen grains stick to the hairs on its body and are carried away when it leaves. When the insect visits another flower, some of the pollen grains are rubbed off onto the stigma, which is positioned at the end of a long stalk called the style at the center of the flower. When the pollen lands on the stigma we say that pollination has taken place. The pollen grows a pollen tube down the length of the style until it reaches the ovary. The nucleus moves down this tube and fuses with the female nucleus (ovule) in the ovary to make a zygote. This fusion of the nuclei is called fertilization.

Wind pollinated flowers (egg the flowers of grass) do not need to attract insects, so they are not brightly coloured, do not produce nectar and have no smell. The anthers hang outside the flower so that the pollen is easily picked up by the wind. The stigma also hangs outside the flower and it has many side branches to act like a net to catch the pollen as it blows past.

The zygote (fertilized ovule) grows to form the seed. The ovary, which usually contains many seeds, will grow into the fruit. The flesh of an apple is a fruit and so is a pod containing beans (which are the seeds). There is little point in a seed growing directly under its parent, because it would be competing for water, sunlight and space. It is best if the seed is dispersed (transported somewhere else). There are many ways of doing this. Some species of plant produce berries that are designed to be eaten by birds. However, the bird cannot digest the seed that passes through the digestive system and out with the faeces (an excellent fertilizer). Some seeds have hooks on the side that stick to the fur of passing animals and only fall off when the animal later cleans itself, which may be many miles from where the seed originated. Other seeds are dispersed by the wind. Some have wings so that they spiral to the ground. Others are very light and have feathery ends so that the wind can carry them great distances. Coconuts have a store of nutrients to survive long journeys as they float across oceans.

You need to know the structure of a bean seed, including: the testa (outer coat), micropyle (small hole where the pollen tube first entered to fertilise the ovule and where water will enter when the seed germinates), cotyledons (the two halves of the bean where starch is stored to feed the growing embryo), plumule (the part of the embryo that will grow upwards to form the shoot) and radicle (the part of the embryo that grows downwards to form the root).

Usually, seeds do not grow as soon as they leave the mother plant. They usually need to wait until the conditions are ideal. For instance, there would be no point in a seed germinating (starting to grow) in freezing conditions or in the middle of the dry season. Such things as temperature, moisture and oxygen are often seed to start germination. Sometimes a seed will lie dormant (still alive, but not growing) for many years before it germinates.

Nervous System

The Vertebrate Nervous System:
1 - receives stimuli from receptors & transmits information to effectors that respond to stimulation
2 - regulates behavior by integrating incoming sensory information with stored information (the results of past experience) & translating that into action by way of effectors
3 - includes billions of nerve cells (or neurons), each of which establishes thousands of contacts with other nerve cells
4 - also includes neuroglia cells that support, nourish, & insulate neurons

Subdivisions of the Vertebrate Nervous System:
1 - Central Nervous System - including the brain & spinal cord
2 - Peripheral Nervous System - including cranial nerves, spinal nerves, & all branches of cranial & spinal nerves

Neurons (or nerve cells):
respond to stimuli & conduct impulses
3 types - all with cell body & processes (axons & dendrites):
multipolar
bipolar
unipolar

Spinal cord:
located in vertebral canal
anatomical beginning is the foramen magnum of the skull
length varies among vertebrates:
in vertebrates with abundant tail musculature, the spinal cord extends to the caudal end of the vertebral column
in vertebrates without tails or without much tail musculature, the spinal cord extends to about the lumbar region of the vertebral column
a cross-section of the spinal cord reveals gray matter & white matter. The gray matter consists of nerve cell bodies, while the white matter consists of nerve cell processes (axons). These processes make up ascending (sensory) and descending (motor) fiber tracts.

Neuronal Structure

Sensory Neurone
The nerve impulses travel from left to right in this diagram of a sensory neurone. A stimulus causes the impulse to be produced by a sense organ. (skin / ears / eyes / tongue / nose)
Dendrites and Synapses are both nerve endings at the ends of neurones. Dendrites are located at the ends that receive the nerve impulses (at the left of diagram above). Synapses are found at the transmitting ends of the neurone where the impulse is transferred to another neurone. Synapses use chemicals to transmit their electrical signal.
Relay Neurone
This neurone does exactly what its name suggests. Relay neurones are situated in the spinal cord. This, along with the brain, acts as the central nervous system.
Reflex actions are caused when a stimulus creates an electrical impulse that is relayed via the relay neurone straight to the effector. The message never actually reaches the brain.
Motor Neurone
A motor neurone is connected to an effector and when an electrical nerve impulse is transmitted, the effector is stimulated into action. (muscles / glands)

Skin and homeostasis

When the body is cold
1. The small capillaries near the surface of the skin constrict (vasoconstriction) so less blood flows nearer to the surface, and less heat is lost through he blood.
2. The hairs on the skin stand erect by the hair erector muscles tightening. The hairs trap a layer of insulating air therefore less heat is lost to the surroundings.
3. Sweat Glands produce less sweat so less heat is lost through evaporation.
The muscles also vibrate very quickly when it is cold, so heat is produced to keep the body temperature at the correct level. This is also known as shivering!
When the body is hot
1. The small capillaries near the surface of the skin dilate (vasodilation) so more blood flows nearer to the surface, and more heat is lost through he blood. The body therefore cools down.
2. The hairs on the skin lie flat because the hair erector muscles slacken. No layer of insulating air is trapped therefore heat can be lost more easily.
3. Sweat Glands produce more sweat so more heat can be lost through evaporation

Responding to changes in the environment

Organisms have receptors (such as eyes, ears, tongues, auxins in plants etc) to detect external stimuli (such as light, sound-waves and chemicals). This enables them to detect what is going on around them and so helps improve their chances of survival.

The human nervous system is made up of the central nervous system (the brain and the spinal cord that are able to made decisions) and many nerves (made up of many nerve cells called neurons) that carry messages from receptors and to effectors. The effector is the organ that carries out the response. Sometimes this can be a gland, but it is usually a muscle. Motor neurons are nerve cells that carry an impulse from the central nervous system to a muscle (you need to know the structure of a motor neuron). A neuron can be very long, with the longest ones reaching from the tip of your toes up to your spine.

It takes a short time for a message to reach your brain, for your brain to think of a response and then for the message to travel to the effector and for it to react. Sometimes this would result in a response that is a little too slow to allow the body to protect itself. This is why, sometimes, the spine can make a simple response of its own. This is known as a spinal reflex arc. The impulse travels up the sensory nerve to the spine. It is then joined by a connector neuron to the motor neuron that immediately sends an impulse to respond. This cuts down the response time.

The rods and cones are cells in the retina that detect light. Rods detect how bright the light is. They are good for seeing at night, but only give a black-and-white image. Cones give a clearer image in colour. There are 3 types of cone: one blue, one green and one red. From these all the other colours can be formed. The fovea has only cones. This is where light is focused when you stare directly at something. It gives a clear coloured image (except when its dark). Around the fovea there is a mixture of rods and cones, giving good vision both in the light and in darkness. The outer parts of the retina have only rods. This is why you cannot see colours in your peripheral vision (although you are usually not aware of this). The rods and cones convert the light stimulus into an impulse, which passes down the optic nerve to the brain, which forms it into an image. There are no rods or cones at that part of the retina where the optic nerve leaves the eye. This area is called the blind spot.

The amount of light entering the eye depends on the size of the pupil, which is controlled by muscles in the iris. Light passes through the cornea then the liquid aqueous humour, followed by the pupil (the hole surrounded by the iris), then the lens, then through the liquid vitreous humour to land on the retina at the back of the eye. In order to see an image this light needs to be focused. The cornea, humours and lens all help to focus the light. However, the lens can vary how much it bends the light. When it is thin (stretched by the ciliary muscles) it does not bend the light very much, so it is good for focusing light from distant objects. When it is fatter it bends the light more, so it is better at focusing on close objects. This ability of the eye to change its focal length is called accommodation.

Plants also have receptors to detect stimuli in their environment and have effectors to respond. One example is phototropism, where a plant grows towards a light source. A hormone called auxin causes this to happen. Auxin is produced in the tips of shoots and promotes growth in the area just below the tip. When light falls on the shoot the auxin moves to the opposite side, away from the light. It then promotes the growth of the cells on that side only, resulting in the shoot bending towards the light.

nutrients in food

There are many different kinds of nutrient in our diet.

Protein
This is an essential body-building food. Much of the structure of cells is protein. Muscles are mostly proteins as are enzymes and hormones. Meat, fish, egg white and milk contain lots of protein. A good source of protein for vegetarians is Soya beans. In many undeveloped countries there is not enough protein in the diet which can prevent normal growth and development.

Fat
Cell membranes are made of fats. Fat also provides a long term store of energy. It also acts as insulation in many animals. Meat, milk and egg yolk contain a lot of fat. Oils are liquid fats. Many plants produce oils such as sunflower oil and olive oil which is used in cooking and to make margarine. It is much healthier to eat plant oils than to eat animal fats, because animal fats are usually much higher in cholesterol, which can cause heart attacks.

Carbohydrate
Starch and sugar are the main types of carbohydrate in the diet. They provide a more immediate source of energy than fats (eg glucose that is used in respiration). The staple diet (the main source of energy) for any population is always starch. In Asia the staple diet is mostly rice; in Britain it is mostly bread (or other products made from wheat flour) or potatoes; in Italy it is pasta and in Central America it is traditionally mainly Maize. Anything sweet contains sugar, such as cakes, sweets etc. Although starch and sugars contain basically the same thing, it is better to eat mostly starch as too much sugar can upset the osmotic balance in your body. Any carbohydrate that is not used is converted into fat for storage.

Vitamins
These are essential chemicals that you need to eat in order for your body to function properly. Vitamin C is needed to help bind the cells together. Without you can get scurvy. Vitamin D is needed so that your body can deposit calcium correctly. A lack of vitamin D leads to Rickets, a disease where the bones lack strength, resulting in the legs bending. Good sources of vitamins are fruits, vegetables and milk.

Minerals
These are inorganic compounds. This means that they do not need to be made by a living thing. If you went to the moon you would find minerals, but you would not find any of the substances mentioned above. Calcium is an example of a mineral that is an important part of our bones and teeth. Iron is another mineral; in this case it is an important part of the haemoglobin in our blood. A good source of calcium is milk. Iron is particularly common in liver and spinach. Many vegetables provide smaller amounts of these vitamins.

Roughage (fibre)
Much of the food we eat cannot be digested and passes right through the gut and is egested in the faeces. Much of this is the cellulose in the cell walls of plants. However, this is still useful because it gives some solid substance to the half digested food in the intestine which makes digestion easier. Without roughage a person can get ulcers, colon cancer and can suffer from constipation. Most roughage is found in fruits and vegetables. Constipation is often the result of eating too much meat and not enough vegetables. Modern packaged foods are often lacking roughage.

A balanced diet includes all of these nutrients in the required amounts. It also includes water. They are not all required in large amounts. Only small amounts of vitamins and minerals are required, but they are still very important. Eating the wrong amounts of these nutrients can be a problem, leading to malnutrition. Eating too much is often as bad as eating too little. In many developed countries people suffer from obesity (being overweight) because they eat too much sugar and fatty foods in their diet. Other parts of the world are lacking one aspect of a balanced diet or they have too little food altogether. The world produces enough food for everyone, but it is often in the wrong places and there are difficulties in distributing it to everyone.

Foods with lots of carbohydrates or fats are high energy foods. If a person eats a lot of this they can put on weight, unless they do a lot of exercise. If you take in more energy than you use you put on weight. If you use more than you take in you lose weight. When someone is dieting they should lower the amounts of fatty foods that they eat and do a bit more exercise. This ensures that they stay healthy. Harsh diets are very bad for the body and can even lead to you putting on more weight in the long run.

Respiration

Glucose is a store of chemical energy. When glucose is broken down into simpler chemicals the energy is released and the cell can use it for such things as movement, growth and warmth. To get the maximum energy out of glucose it is best to react it with oxygen to produce carbon dioxide and water. This is called Aerobic respiration.

Aerobic respiration

Glucose + Oxygen ----Carbon dioxide + Water + released energy

For short spells it is possible for human cells to respire without any oxygen. For instance, when an athlete runs 100m there is no time for the body to get enough oxygen to all of the muscles. In this case the cells do anaerobic respiration, which is respiration without oxygen. The cells convert the glucose into lactic acid and a small amount of energy is released. Lactic acid is harmful in the body, so humans cannot respire this way for very long. Afterwards the lactic acid needs to be removed and this requires oxygen (it is known as the oxygen dept). This is why an athlete pants after a race.

Respiration is one of the characteristics of living things. If a cell does not respire then it is not alive. Therefore, plant cells respire and animal cells respire and so do bacteria cells and fungi cells.

Gaseous Exchange in Animals

Larynx ? this is the Adam?s apple, which is where the tube in your throat splits up into 2: the trachea that takes air to and from the lungs and the esophagus that takes food to the stomach.
Trachea ? this tube has rings of cartilage that stop it from closing over (you can feel them in your throat. This ensures that air can always pass through.
Epiglottis ? this is a flap that is found in the larynx. Usually it closes over the oesophagus, but when you swallow it closes over the trachea to stop food going into your lungs (sometimes food or drink does go down the wrong tube and makes you cough).
Bronchi ? there are 2 lungs, so the trachea splits up into 2 bronchi: one for each lung.
Bronchioles ? the bronchi divide up into a network of tiny tubes called bronchioles.
Alveoli ? the bronchioles end on groups of small air sacs called alveoli (one is called an alveolus). This is where gas exchange takes place.
Pleural membranes ? it is important that the lungs do not rub on the inside of the chest. The pleural membranes prevent this.
Diaphragm ? this thin layer of muscle separates your thorax (chest cavity) from your abdomen (the area with most of your guts). When it contracts it increases the volume of the thorax and causes air to enter the lungs.
Intercostal muscles ? these are the muscles between the ribs. When they contract, they pull the ribs upwards and outwards to increase the volume of the thorax.

Gas exchange
The exchange of gases takes place in the alveoli. Oxygen crosses from the air in the alveoli to the haemoglobin in the blood. Carbon dioxide crosses in the other direction, from the blood to the alveoli.
The alveoli are especially designed to allow this to happen (again, it would help here to check a diagram). There are large numbers of blood vessels surrounding the alveoli; the alveoli and blood vessels both have thin walls (only one cell thick), so it is easy for gasses to diffuse through; the surfaces are moist, which allows the diffusion to take place more easily; the alveoli provide a large surface area for diffusion to occur. If the lungs were just bags, there would only be a very small amount of surface to exchange gasses, but the alveoli provide a surface area equal to about the size of a tennis court.
The gasses move across the surface by diffusion. Remember that this is the movement of particles from an area where it is highly concentrated to an area where it is less concentrated. Remember, also, that the membrane does not carry the particles across, they just move across randomly.

Inhaling and exhaling (again, check your handouts)
When you inhale (breath in), one set of intercostals muscles contracts pulling the ribs upwards and outwards, which increases the volume of the thorax (chest). At the same time the diaphragm contracts, which further increases the volume. This means that the air in the lungs is now taking up a bigger space, so it will be at a much lower pressure. The air outside the body is now at a higher pressure, so when you open your mouth the outside air pressure forces air to enter your lungs.
When you exhale, the opposite happens. The intercostals muscles pull the ribs downwards and inwards and the diaphragm relaxes, causing the volume of the thorax to decrease, which increases the pressure, forcing air out of the mouth.

Keeping the lungs clean
When you breathe in there are often small particles in the air and bacteria that enter your lungs. These can be harmful and need to be cleaned out. The surface of the lung has cells called goblet cells that secrete a sticky substance called mucous. The particles in the air stick to the mucous which can then be removed. This is done by the cilia, which are tiny moving hairs lining the surface of the lungs. The cilia waft the mucous and particles up the bronchi and trachea where it is usually swallowed. Coughing is a way of removing mucous from the lungs.

Smoke and air pollution
Although the lungs can clean some substances from the lungs, if there is too much it can cause serious damage. Many air pollutants can damage the delicate cells inside the lungs. The effect depends a lot on the type of pollutant that is present, but commonly the person will cough a lot and the efficiency of gas exchange will be less.

Smoking
Cigarettes contain a number of chemicals. Nicotine is the main drug that is found in cigarettes and it acts as a depressant, which means that it calms the body. Nicotine is also highly addictive, so many people smoke because they have a need caused by the addiction rather than getting any useful affect. A number of serious problems can be caused by smoking. The biggest danger is from lung cancer, but many other diseases such as emphysema, bronchitis, heart disease and a whole load of other problems, are associated with smoking. One problem is that the cilia lining the lungs stop being formed, so the lungs are not able to clean themselves. This means that the dangerous chemicals build up and have a greater effect. When someone gives up smoking the cilia grow back and start cleaning the lungs again. Smoking also affects the efficiency of the lungs, so smokers often get short of breath very quickly when they do exercise.

cells and function- plant cell

Plant cell: the cell is a highly complex system that is the site of intense energy exchange and which presents vast interphase surfaces. Like all living organisms, it feeds itself, grows, multiplies and dies.

Plasmodesma: intercellular bridge.

Dictyosome: cellular organelle that elaborates sugars and proteins.

Chromatin: a colouring substance in the nucleus of the cell.Nucleus: small spherical body with the cell nucleus.

Nuclear envelope: membrane surrounding the nucleolus.Endoplasmic reticulum: a formation within the cytoplasm that plays a role in the production of various substances.Peroxisome: cytoplasmic organelle which contains enzymes.Chloroplast: granule of chlorophyll, which is needed for photosynthesis.

Mitochondria: granule that plays an important role in the respiration and energy-releasing reactions in living cells.

Cytosol: liquid part of the cytoplasm.

Free ribosome: cytoplasmic organelle which is responsible for protein synthesis.

Tonoplast: vacuolar membrane.Vacuole: space with the cytoplasm of a cell containing various substances.

Cell wall: cell wall.

Plasma membrane: envelope of plasma.

Thylakoids: membranous molecular structures involved in photosynthesis.

Starch grain: starch granule.