Science and Technology

Plants are living things. We can classify (sort) plants into groups using features we can see. In Grade 5 we sort plants into two main groups: flowering plants and non-flowering plants.

Flowering plants grow flowers, which later form fruits and seeds. Most plants around us are flowering plants. Examples in Kenya include maize, beans, mango, pawpaw (papaya), sukuma wiki (kale) and the jacaranda tree.

Non-flowering plants never grow flowers. Instead, many make new plants from tiny spores. Examples include mosses and ferns that grow in cool, damp places, and algae that float in ponds and rivers.

To tell the groups apart, look for:

• Flowers, fruits and seeds — only flowering plants have these
• Green, low, feathery leaves and no flowers — often ferns and mosses

Sorting plants helps farmers, scientists and herbalists know how to grow and use them.

Vertebrates are animals that have a backbone (also called a vertebral column) inside their bodies. The backbone is a row of small bones running down the back. It supports the body and protects the spinal cord. Scientists sort vertebrates into five groups:

• Mammals — have hair or fur, breathe with lungs, and feed their young on milk. Examples: cow, goat, dog, human, elephant.
• Birds — have feathers, wings and a beak, and lay eggs. Examples: chicken, weaver bird, ostrich.
• Fish — live in water, have scales and fins, and breathe using gills. Examples: tilapia, Nile perch.
• Reptiles — have dry, scaly skin and lay eggs on land. Examples: lizard, snake, crocodile, tortoise.
• Amphibians — have moist skin and live partly in water and partly on land. Examples: frog, toad.

On a Kenyan farm you can find mammals (cattle), birds (chickens) and reptiles (lizards) all in one place.

Breathing is taking air into the body and pushing it out again. We breathe to get oxygen, a gas our bodies need to stay alive, and to remove a waste gas called carbon dioxide.

The main parts of the breathing system are:

• Nose — air enters here and is warmed and cleaned
• Trachea (windpipe) — a tube that carries air down to the chest
• Bronchi — two tubes, one going into each lung
• Lungs — two spongy organs where oxygen passes into the blood
• Diaphragm — a sheet of muscle below the lungs that helps us breathe

When we breathe in (inhale), the diaphragm pulls down and the chest gets bigger, so air rushes into the lungs. When we breathe out (exhale), the diaphragm relaxes and pushes air out.

You can feel this yourself: place a hand on your chest and take a deep breath after running — it moves as your lungs fill with air.

A mixture is formed when two or more substances are put together but do not change into new substances. The parts of a mixture keep their own properties, so they can be separated again. For example, a plate of githeri (maize and beans) is a mixture — you can still pick out the maize and the beans.

We separate mixtures using the method that suits the materials:

• Hand picking / sorting — for large pieces, e.g. removing stones from beans
• Sieving — passes small grains through holes, e.g. sifting flour from husks
• Winnowing — wind blows away light husks from heavier grain
• Filtration — separates solids from a liquid, e.g. tea leaves from tea
• Decantation — pouring off clear water, leaving sand at the bottom
• Using a magnet — picks out iron pieces from a mixture

Choosing the right method depends on the size, weight and properties of each part. Separating mixtures helps us clean food, water and other materials at home.

Water pollution happens when harmful or unwanted materials get into water and make it dirty and unsafe. Clean water should be clear, colourless and free of harmful things.

Causes of water pollution include:

• Throwing rubbish and plastics into rivers and lakes
• Sewage (human and animal waste) flowing into water
• Waste and chemicals from factories
• Farm chemicals such as fertilisers and pesticides washed into rivers
• Oil and soapy water poured into drains

Polluted water is dangerous. It can cause diseases such as cholera and typhoid when people drink it. It also kills fish and other water animals, and makes water unfit for farming.

We can help keep water clean by putting rubbish in dustbins, not washing directly in rivers, treating sewage, and planting trees near rivers. In many Kenyan homes, people are told to boil or treat drinking water to stay safe. Protecting water keeps our families and the environment healthy.

When we put objects in water, some float (stay on top) while others sink (go down to the bottom). Water pushes up on every object with a force called upthrust. If the upthrust is strong enough to hold the object up, it floats; if not, it sinks.

Whether an object floats or sinks depends on:

• The material — a piece of wood floats, but a stone of the same size sinks because the stone is heavier for its size (it is denser)
• The shape — a flat metal sheet can be shaped into a bowl that traps air and floats
• Trapped air — objects holding air, like a plastic bottle with the lid on, float

This is why a heavy metal ship can float: it is shaped to hold a lot of air. An empty jerrican or a tyre tube floats and can help someone stay above water, while a solid metal spanner quickly sinks.

Sound is a form of energy that we hear with our ears. All sounds are made when something vibrates (moves quickly back and forth). When you beat a drum, the drum skin vibrates and makes the sound; when you speak, parts inside your throat vibrate.

Sound travels away from its source in all directions as sound waves. It needs something to travel through, called a medium — this can be a solid, a liquid or a gas. Sound travels fastest through solids and slowest through gases like air. Sound cannot travel through empty space (a vacuum) because there is nothing to carry it.

Some sounds are loud and others are soft. Very loud sound, called noise, can harm our ears. We can control noise by lowering the volume, closing windows, or moving away from the source.

For example, when a teacher rings the school bell, the metal vibrates and the sound travels through the air to reach every learner.

Heat is a form of energy. Heat always moves from a hotter place to a cooler place. There are three ways heat can travel:

• Conduction — heat moves through a solid as it passes from particle to particle. When you stir hot uji with a metal spoon, the handle becomes hot. Metals are good conductors of heat.
• Convection — heat moves through liquids and gases as the warm parts rise and the cooler parts sink, making a flow. This is how water heats up in a sufuria on the fire.
• Radiation — heat travels as invisible rays through empty space, with no medium needed. This is how heat from the Sun and from a fire reaches us.

Materials that do not let heat pass easily are called insulators, for example wood, plastic and cloth. That is why cooking pots have wooden or plastic handles — they stay cool so we do not burn our hands.