Two-thirds of Earth's surface is covered with water in the form of oceans, ice caps, lakes, and rivers. All living things need water because 75 percent of their bodies are made of it. All internal changes in living things occur in the form of solutions.
About 21 percent of Earth's atmosphere contains oxygen. Most living things need oxygen for respiration, which helps produce energy for various activities of the body.
Sunlight provides energy for all living things. Plants use sunlight to make food by photosynthesis. Animals get energy indirectly from green plants, either by eating them or by eating animals that eat plants.
There is about 0.04 percent carbon dioxide (CO2) in the atmosphere. It is constantly being increased by the respiration and excretion of animals, as well as the burning of wood and coal. Plants use carbon dioxide as a raw material for making their food.
All heat energy on Earth comes from the sun. Temperatures vary in different places around the world based on their proximity to the sun. Most plants and animals are adapted to live in a particular temperature range. For example, lions and tigers are adapted to live in hot places, while polar bears and penguins are adapted to live in cold places. If the surroundings become too hot or too cold, chemical changes taking place inside their bodies stop, and the organisms die.
All living things are made up of cells. A cell is the smallest part of a living thing that can carry out life's activities. Cells are the building blocks that all living things are made up of. For example, your body is made up of trillions of cells. The different kinds of cells are plant cells and animal cells. The cells that plants are made up of can make food for the plants, and they can store water too. The cells that make up animals allow for taking in food since animals do not make their own food.
Look inside this animal cell, what job does each part have?
Nucleus: A large, round part that acts as the control centre of the cell. It regulates the cell's growth and reproduction.
Cytoplasm: A gelly-like material inside the cell that holds all the inner parts of a cell.
Mitochondrion: The power plant and the organelle that generates energy for the cell through a process called cellular respiration.
Cell membrane: The thin outer layer of the cell that lets things in and out of the cell.
Vacuole: A membrane-bound cell organelle. Animal cells usually have tiny vacuoles that help store and dispose of various substances.
Plant cells have the same parts that animal cells have. However, vacuoles in plant cells are a little different from those in animal cells. Plant cells have two additional parts as well.
Vacuole: larger than a vacuole in an animal cell. This is a cell part that holds a lot of water and gives shape to the cell.
Cell Wall: a hard outer layer of a plant cell that protects the cell and provides support.
Chloroplast: a part of a plant cell that uses energy from sunlight to make food.
The table below depicts the functions and characteristics of various organelles found in animal and plant cells. Some of these features are common to both animal and plant cells, but others are unique to plant cells.
| Cell structure | Function | In animal cell | In plant cell |
|---|---|---|---|
| Cell membrane | Controls the exchange of material between the cell and its surroundings. | Yes | Yes |
| Nucleus | Contains DNA arranged in chromosomes and regulates cell activities. | Yes | Yes |
| Cytoplasm | Jelly-like substance where chemical reactions of the cell occur. | Yes | Yes |
| Cell wall | Made of cellulose. It protects the cell and gives it its shape. | No | Yes |
| Chloroplast | Contains chlorophyll which helps the plant to produce food by a process called photosynthesis. | No | Yes |