Plant Systems - Science Lessons for Grade 5 Students
The two main systems in plants are the root system and the shoot system. Each system helps the plant in different ways. The root system usually refers to the organs that grow below the soil, whilst the shoot system refers to the organs that grow above the ground. A plant needs these two systems to work alongside each other in order to be alive and healthy. For example, the root system allows the plant to take water and nutrients from the soil, but the shoot system allows these to move to other parts of the plant like the leaves. Let us look at these two systems in detail.
The root system
The root system has two parts – the roots and root hairs. The roots of a plant usually grow downwards into the soil. The root system helps the plant in two main ways:
- It helps to hold the plant in the soil.
- It helps to take in water and minerals from the soil and carry them to other parts of the plant.
Though the majority of plants have their roots underground, some plants have roots that develop from the shoot above the soil.
Types of roots
The tap root and the fibrous root are the two main types of roots in plants. Some plants such as grass and the African Violet have roots that branch out in all directions. They are called fibrous roots. Other plants, such as carrots and dandelions, have one main root with smaller side roots. They are called tap roots.
The shoot system
The shoot system has four parts – the stem, leaves, flowers and fruits. The stem of a plant usually grows upwards.
The stem joins the roots to the upper parts of the plant. It holds up the leaves so they can absorb sunlight. It also carries water and minerals from the roots to all parts of the plant. Moreover, it carries food from the leaves to all parts of the plant. The stem is able to do this because inside the stem are tubes that carry water and food to the other parts of the plant. Stems of plants can be a few millimetres long or hundreds of metres long. Their diameter differs depending on the plant variety.
Most leaves are green in colour. They come in different shapes and sizes. Green leaves make food for the plant using water, carbon dioxide and energy from sunlight. This process is called photosynthesis. Most leaves are green in colour because of the presence of a pigment called chlorophyll.
Leaves have functions other than making food for the plant. It is through the leaves that the plant loses water. In this way, the plant is able to regulate its temperature and absorb more water from the bottom of the root. Though the leaf is part of the shoot system it works only if the root system carries out its role.
Flowers come in many different shapes, sizes and colours. Although they look different, they have similar parts. The stamen, the male part of the flower, has a filament and an anther. The anther makes pollen which is used in reproduction. The female part of the flower, the pistil, has a stigma, a style, an ovary and ovules. The ovules become seeds.
Plant reproductive organs, the stamen and the pistil, are both present in the flowers of plants. The majority of plants have both male and female sexual organs in the same flower, but some plants have some flowers that are completely female and other flowers that are completely male.
Fruits and seeds
When flowering plants reproduce, the petals dry up and drop off. The ovary changes into a fruit. The ovules become the seeds. Fruits come in a range of different shapes, sizes and colours. Many fruits have the same basic parts. They have a stalk, sepals, a fruit wall and seeds.
Some fruits contain only one seed. They are called one-seeded fruits. Other fruits contain many seeds. They are called multi-seeded fruits. Examples of one-seeded fruits include mangoes and avocadoes. Examples of multi-seeded fruits include papaya and beans.
Fruits can be fleshy or dry. Fleshy fruits have soft and juicy fruit walls. They usually contain a lot of water. Dry fruits have dry fruit walls and do not contain much water.
Some types of fruit such as papayas, oranges and mangosteens can be eaten by people. These fruits are called edible fruits. Other types of fruits that cannot be eaten by people are called inedible fruits.