SCIENCE STD 7 (NOTES)

Many thousands of years ago, people began to find ways of changing the simple materials they found around them into more useful forms that could enhance their lives. Human beings are able to turn materials of the natural world into tools, food, machines, systems and processes that can help them live better. Technology is the science and art of making and using materials and resources around us. It is the application of scientific knowledge and discoveries to improve our way of life. Human technology involves seeing new needs, finding new ways of meeting them, and appreciating the value of accidental discoveries.

OBJECTIVES

Describe technology as the application of scientific knowledge and discoveries.

Classify objects as natural or man-made.

Demonstrate proper use of simple technology such as a watch, a telephone, a camera, a cell phone, a computer etc.

Explain the impact of technology on agriculture, medicine and space science.

Describe how technology contributes to solving problems.

Identify problems caused by technology.

Technology rearranges the world to suit our needs. Not every technology is a response to need. Often scientists or engineers discover or create things that have no apparent use, but develop them anyway out of curiosity to see what will happen.

Agriculture

Technology has used microscopic organisms for many years. Brewing and baking make use of yeast.

Medicine

Some of the greatest advances in technology have been in diagnostic machines that help doctors see what is wrong, and in improved equipment to carry out surgery and keep patients alive while it is going on.

Space Science

Technology had enabled men to study the world beyond his immediate environment and to study the earth from high up. 

OBJECTIVES

Describe technology as the application of scientific knowledge and discoveries.

Classify objects as natural or man-made.

Demonstrate proper use of simple technology such as a watch, a telephone, a camera, a cell phone, a computer etc.

Explain the impact of technology on agriculture, medicine and space science.

Describe how technology contributes to solving problems.

Identify problems caused by technology.

Feeding Relationships: Scavengers and Decomposers

Scavengers are other animals in the food chain that feed on carcasses. Most scavengers do not kill their own prey, rather they depend on leftovers left by predators. Examples include hyenas, vultures and foxes. Scavengers normally live side by side with predators so that they can always have the leftovers.

When living things, both plants and animals die, they start to rot, the process of decomposition begins. Other living things such as maggots, bacteria and fungi begin to feed on the decomposing body. Organisms that feed by breaking down dead bodies or waste material are called decomposers. The whole decomposition process therefore is also part of food chains and food webs, in that these decomposing plants and animals provide food for other living things, which in turn will be a source of nutrients for something else.

When an organism or part of an organism dies, the compounds it contains can be passed on to soil bacteria and fungi as their food. Decomposers release carbon dioxide into the air when they respire. Some of the energy from decomposition is released into the surroundings. Plants and animals need a constant supply of carbon to make carbohydrates, proteins and fats to stay alive.

Scavengers and decomposers are normally found at the end of the feeding relationships. This is important because they rid the environment of dead matter and provide natural sanitation. Otherwise the land and oceans would be full of carcasses

Decomposers are animals that break down or decay or rot organic matter (dead plants and animals remains) into simpler chemical substances. The breaking down of organic matter into simpler chemical substances is called decomposition.

Germination covers all the processes that occur from the time of planting a dry seed to the growth of a young plant. When a seed germinates, it begins by taking in water through the mycropyle. The water dissolves the enzymes in the cotyledons. The enzymes digest the stored food, and make it soluble. The soluble food then diffusesinto the plumule and radicle making them grow. The radicle grows first and pushes into the soil to absorb water and minerals. The plumule pushes upwards. When it breaks out above the soil, into the light, it becomes green and begins tophotosynthesise. The growing seed relies on its food stores in the cotyledon until it can make its own food. Once anchored in the soil, green leaves open out and begin to photosynthesise.

Germination requires water, suitable temperature and oxygen, but not light. Oxygenfrom the air enters the seed through the micropyle and later through the rupturedtesta. The enzymes in the cotyledons can only be activated at a certain temperature, so a suitable temperature must be reached before germination can start.

OBJECTIVES

Describe seed germination.

Investigate conditions necessary for seed germination.

After seeds are formed they must be dispersed if the new plants are to survive. Seed dispersal is the spreading out of the seeds as far away as possible from the parent plants.

This contributes to the spread and continuance of species. In some species only the seeds are dispersed, while in others the fruits are dispersed with the seeds. Dispersal is important for the following reasons:

It prevents overcrowding

It reduces competition for light and nutrients

It enables plants to colonise new localities

It reduces epidemic diseases among crowded seedlings.

It increases the chances of a young plant surviving.

OBJECTIVES

Define seed dispersal.

Describe the different modes of seed dispersal.

Identify seeds and fruits according to their modes of dispersal.

Adaptation describes the characteristics of an organism that help it to survive in a particular habitat. Animals and plants are adapted in different ways to different environments.

OBJECTIVES

Define adaptation.

Describe ways by which different plants are adapted to their environment.

Explain how these adaptations help the plants to survive.

Water is one of the most important natural resources in life. Without water all animals and plants will die. You can survive longer without food than without water. However not all water is good for human consumption. Some water may contain harmful micro-organisms that may cause diseases when swallowed. It is therefore important that the water is treated before it can be used for consumption. This ensures that diseases from the water are not transmitted to people.

OBJECTIVES

Describe the process of water purification in towns.

Demonstrate ways of making water safe to drink.

Discuss the importance of decontaminating water.

At any one time of the day, half of the earth has light, while the other half is in darkness. The parts of the Earth’s surface that face towards the Sun are lit by it and experience day while the parts of the Earth’s surface that face away from the Sun are in darkness and experience night. The day and night cycle is caused by the rotation of the Earth about its axis. Because the Earth always rotates in the anticlockwise direction, the Sun always appears to rise at dawn generally towards the East and sets at dusk, generally towards the west. The Earth rotates once every 24 hours and this is how our day is defined.

OBJECTIVES

Distinguish between rotation and revolution of the Earth.

Explain day and night in terms of the Earth’s rotation on its axis.

Describe the motion of the Earth around the Sun.

Discuss seasons in relation to the motion of the Earth around the Sun.

Cooling

Normally a substance will cool if the temperature of its surroundings is less than the temperature of the substance. The heat energy is transfer from the substance to the surroundings. When a substance cools down, its kinetic energy decreases and the molecules move closer together. This results in a decrease in the temperature and volume of the substance.

Evaporation

In liquids, cooling can be brought about by evaporation. When the liquid on the surface escapes it takes some of the heat energy away with it. This is because the particles with more energy rise to the surface of the liquid and escape into the air. In doing so they take away the heat energy and the temperature of the liquid decreases. As more of the liquid evaporates from the surface, the liquid remaining in the container becomes cooler.

Energy is the ability to do work. Every activity or process requires energy. Animals get their energy from the food they eat. Most of our energy needs today are met by burning fuels. Crude oil is the most extensively used form of energy source today. It provides about two thirds of the world energy needs. Unfortunately, once finished, it cannot be replaced. We call such an energy source non-renewable energy source. Other non-renewable energy sources are coal, natural gas and nuclear energy. It is therefore important that alternative energy sources are identified and used. Alternative energy sources, also called renewable energy sources are:

Biomass: energy from animal and plant matter.

Solar energy: energy from the sun

Wind energy: energy from moving air

Hydroelectric energy: electrical energy produced from falling waterTidal energy: energy from ocean tides

Wave energy: energy from sea waves.

These are called renewable energy sources because they can be used again and again without finishing them. That is, they cannot be run out like crude oil, natural gas, coal and nuclear energy.

Biomass, solar energy and wind energy are readily available to most people in Botswana. These energy sources are cheap to use. They are easily accessible and do not cause pollution.

OBJECTIVES

Identify renewable energy resources in Botswana.

Discuss uses for such energy sources.

Discuss the social and economic benefits of harnessing solar energy, biomass and wind energy.

Harness solar energy in whatever way to heat water.

Heat Transfer

Heat can move from one end to another end. It always moves from a body of high temperature to a body of low temperature. Heat can move either by conduction,convection or radiation or by a combination of two or all the processes.

Heat Conductors and Insulators

Different materials carry heat differently. Some materials carry heat easily, while others cannot. Those materials that allow heat to pass through them easily are called heat conductors. Such materials transfer heat mainly by conduction. Solids, especially metals, are good conductors (poor insulators). However, some solids are very poor conductors of heat e.g. wood and paper.

Those materials through which heat cannot pass through easily are heat insulators.It is difficult for these materials to transfer heat by conduction. Liquids and gases aregood insulators (poor conductors). Gases are particularly good insulators than solids and liquids. Thus air is a very poor conductor of heat and therefore it makes a very good insulator.

OBJECTIVES

Distinguish between heat conductors and insulators

Identify building materials that are conductors.

Identify building materials that are insulators.

Construct a heat retainer using locally available materials.

Light and Sight.

Eyes are some of our most important sense organs. We need eyes to function effectively. Our eyes alone cannot see if there is no light. Eyes receive light and give us sight. Light is the stimulus for our sense of sight. That is, a person with vision can only see when there is light. That is why you cannot see in a darkroom. The eye has an opening called pupil, that controls the amount of light entering the eye.

Structure of the eye

The eye is a large organ made of different tissues. Eyes rest in sockets in the skull and are protected by the skull bone. Eyes also have a liquid inside that holds their shape and help to bend light rays. Different parts of the eye have different functions.

Eyelid: prevent objects from entering the eye

Cornea: bends light to form images in the eye

Iris: coloured part of the eye that opens and closes to control the size of the pupilPupil: opening in the eye that controls amount of light entering the eye.

Lens: focuses light rays on the retina to form images

Ciliary muscles: controls the size and shape of the lens to focus light.

Retina: a place where images are formed inside the eye.

Optic nerve: carries electrical messages (nerve impulses) from the retina to the brain.

We see objects when light passes through the pupil and is focused on the retina by the lens. The retina has sensory cells that convert light into electrical messages that are sent to the brain through the optic nerve. The brain interprets the massage and tells us what we see.

OBJECTIVES

Show that light is needed for one to see.

Correctly label the eye.

State the functions of parts of the eye (i.e. pupil, iris, lens, cornea, retina, optic nerve, and eyelids).

Describe the appearance of the pupil in response to different amounts of light.

Discuss factors that may cause visual impairment.

Eyes are some of our most important sense organs. We need eyes to function effectively. Our eyes alone cannot see if there is no light. Eyes receive light and give us sight. Light is the stimulus for our sense of sight. That is, a person with vision can only see when there is light. That is why you cannot see in a darkroom. The eye has an opening called pupil, that controls the amount of light entering the eye.

We see objects when light passes through the pupil and is focused on the retina by the lens. The retina has sensory cells that convert light into electrical messages that are sent to the brain through the optic nerve. The brain interprets the massage and tells us what we see.

The ear is another sense organ that we need to function effectively. The ear enables us to detect different sounds and respond accordingly. However, even a person with normal hearing cannot her all sounds. Some sounds are too low for the human ear to detect and others are too high. Different animals have different hearing levels. The average human being can detect sounds with a frequency of between 20Hz to 20 000Hz.

Structure of the ear.

The ear is made of different parts that work together to enable it to hear. The ear can be divided into three major areas:

The outer ear: consists of the ear flap (pinna), ear canal and ear drum.

The middle ear: small bones (ossicles)

The inner ear:

A chemical reaction is when a substance breaks down to form new substances or when substances combine to form a completely new substance or substances. In every chemical reaction there is a chemical change. Every time there is a new substance that is chemically different and unique.

Chemical reactions occur all around us in the natural world, in industry and in the home. Chemical changes happen anywhere where materials are changed and new substances produced. Cooking food, washing clothes with soap, burning fuels, rusting iron, brewing beer and making sour milk are all examples of chemical processes. If you strike a match, the reaction produces several products including carbon dioxide and water as well as heat and light.

We use machines in most of our daily activities. A machine is a device that helps us to do things more easily. Machines help us do more work with less effort. We use simple machines to make our work easier. Simple machines can be divided into pulleys, inclined planes, wedges, wheel and axle, and gears.

Pulley: is a simple machine with one or more grooved wheels and a rope. A pulley can be used to lift heavy objects. Pulleys are used in lifts (elevators) in tall buildings and in escalators. They are also used by mechanics to lift vehicle engines. Less effort is needed to lift a load if two or more pulleys are used.

Gears: are toothed wheels that link with similar wheels to transfer or change the direction of a force. The teeth on the gears usually mesh with one another and rotating one wheel causes the other to rotate. In a bicycle the teeth do not mesh. Instead they are linked by a chain going round each gear. Gears of different sizes have different numbers of teeth. The force and speed that is passed on to the other gear depends on sizes of the gears. A large gear will always move more slowly than a small gear that drives it, but can exert more force.

Inclined plane: a sliding surface use to load heavy objects. The load is pushed up the inclined plane. It requires less effort to push the load up the slope than to lift it directly.

Wedge: is a simple machine consisting of two inclined planes joined together e,g.axe, chisel etc. A wedge is used to split wood or rock

Wheel and axle: is a simple machine in which a wheel is joined to an axle. With this type of machine applying a force to the axle causes the wheel to go round as used in awindglass to draw water from a borehole.

Unhealthy eating habits

Eating well means having a balanced diet, eating enough of each of the food groups and not having too much fat sugar or salt. If you ate foods like burgers, fried chips, fat cakes, Russians, chocolates etc it could make you very unhealthy. Such foods may lead to too much fat accumulating in the body leading to a condition called obesity. This condition is becoming very common in most parts of the world including Botswana. Obesity may lead to other health problems such as high blood pressure(hypertension).

Getting fit is not just about training and exercising. Fitness is about how we eat, look after ourselves and keep the organs and organ systems in good condition. If we are going to remain fit and healthy, we must eat a balanced diet, do a reasonable amount of exercise, not drink alcohol and smoke, and not take drugs other than those prescribed for us.

Deficiency Diseases

A balanced diet provides the correct amounts of nutrients, in the right proportions for all our needs and for maintaining good health. Lack of proper diet may generally result in people suffering from serious diseases. Food that we eat must contain vitamins and minerals to prevent deficiency diseases. These are diseases that people suffer from because of lack of certain nutrients in their diet. The table lists examples of such diseases and their causes. These diseases can easily prevented by taking small amounts of the necessary mineral or vitamin in the diet.

The nervous system works to control and coordinate almost every action that the body performs. It does this in response to both external and internal stimuli. The entire nervous system consists of specialised nerve cells called neurones. Neurones have the ability to transmit nerve impulses very quickly, about 100 m per second. The nervous system can be divided into two main parts.

the central nervous system (CNS);

the peripheral nervous system (PNS).

The central nervous system is made of the brain and spinal cord. It receives information from the peripheral nervous system, processes it, and makes decisions which are then transmitted back through the peripheral nervous system as feedback for action. Humans have a complex and highly developed brain than any animal known.

The peripheral nervous system consists of bundles of nerve fibres or nerves which lead to and from the central nervous system. Within the peripheral nervous system there are two types of neurones:

sensory neurones

motor neurones

OBJECTIVES

Identify the major organs of the nervous system

Describe how the nervous system works.

Identify the central nervous system (CNS).

Describe the difference between a reflex action and a voluntary action.

During sexual intercourse, genital fluids of the man and woman come into contact. When the vagina or penis are/get bruised or cut, the openings predispose the individuals to sexually transmitted infections. Sexually transmitted diseases further predispose individuals to HIV and AIDS infection. The sore or openings that caused by the disease, leave the blood exposed therefore vulnerable to cause or receive infection of HIV and AIDS. For instance if an individual has herpes, the open herpes sores make it possible for the body fluids and blood of partners to mix and possibly result in HIV infection if one of the individuals has an HIV

There are so many sexually transmitted infections but the following are very common in Botswana; Gonorrhoea, syphilis, genital herpes, abnormal vaginal discharge, genital warts, genital ulcer, Chlamydia, hepatitis B. These diseases are transmitted during sexual intercourse.

OBJECTIVES

List common sexually transmitted infections in Botswana

Describe how sexually transmitted diseases increase the risk of contracting HIV and AIDS.

Identify diseases that are closely associated with HIV and AIDS infection.