Plant Parts & Functions PDF

# PLANTS AROUND US Based on the size and type of stem, plants can be grouped into trees, shrubs, herbs, creepers and climbers. ## Trees: Trees are tall plants with a thick, strong stem called **trunk**. These have many branches growing from the upper parts of the tree. Trees live for many years,...

# PLANTS AROUND US Based on the size and type of stem, plants can be grouped into trees, shrubs, herbs, creepers and climbers. ## Trees: Trees are tall plants with a thick, strong stem called **trunk**. These have many branches growing from the upper parts of the tree. Trees live for many years, some even up to hundreds of years. Banyan, mango and coconut are a few examples of trees. ## Shrubs: Shrubs have a hard, brown stem. They also have many small woody branches and live for several years. Hibiscus, rose and jasmine are a few examples of shrubs. ## Creepers: Creepers have very weak stems that grow along the ground. Pumpkin and watermelon are a few examples of creepers. ## Climbers: Climbers have weak stems and cannot stand erect on their own. These plants need support of walls or sticks. Grapevine, money plant and pea are a few examples of climbers. ## Herbs: Herbs are small plants with soft, short and flexible green stems and a few branches. These plants live for a few months. Grass, coriander, mint, rice, wheat and spinach are a few examples of herbs. # PARTS OF A PLANT The parts of the plant found below the ground are called the **root system**. The parts of the plant found above the ground are called the **shoot system**. ## Root System: There are two types of root systems: taproot system and fibrous root system. ### Taproot System: Taproot (Fig. 8.1) is a single root that comes out from the seed after germination. Taproot grows vertically downwards into the soil to obtain water from deep down into the soil. It is also called the main root or the primary root. It gives out several smaller branches called lateral roots or secondary roots. Plants such as neem, mango, pea, carrot, radish, turnip and mustard have taproots. ### Fibrous Root System: The fibrous root system (Fig. 8.2) does not have a single main root. It has a cluster of thin fibre-like roots that develop from just below the stem. These roots do not grow very deep into the soil. Plants such as maize, wheat, sugarcane, rice and grass have fibrous roots. ### Functions of Roots: * Roots hold or anchor the plant firmly to the soil. * Roots help plants to absorb nutrients and water from the soil. * Roots prevent soil erosion by binding the soil particles together. ## Shoot System: The part of the plant that grows above the ground is called the shoot system. The stem is the main part of the shoot system and bears the branches, leaves, buds, flowers and fruits. ### Stem Stem is the connection between the roots and the other parts of the plant. It exposes branches, leaves and flowers to sunlight. It also supports the plant. The point on the stem from where a leaf, a branch or a bud grows is called a node. There are many nodes on the stem. The portion of the stem between two nodes is called an internode. Stem has buds, which grow into a leaf, flower or branch. The bud at the tip of the plant is called apical or terminal bud. Apical bud is responsible for the growth of the plant. The bud present at the nodes is called axillary or lateral bud (Fig. 8.9). ### Functions of the Stem: * It provides support to different parts of the plant and holds the plant upright. * Stem helps branches and leaves to spread out. This helps the leaves to receive sufficient sunlight to carry out photosynthesis. * Stem transports water and minerals from the roots to the It also carries food manufactured by leaves to different parts of the plant. ### Modifications of Roots: In some plants, the roots are modified to perform special functions according to the needs of the plant. Some of the root modifications are given below. 1. **Food Storage:** Roots of some plants become fleshy to store food. Carrot, beetroot, radish, turnip and sweet potato are some of the modified roots that we eat as food (Fig. 8.3.) 2. **Extra Support:** In plants such as banyan tree, a large number of roots are produced from the upper part of the stem or from the branches. These roots grow downwards and penetrate into the to provide support. These roots are called **prop roots** or **aerial roots** (Fig. 8.4). In plants such as maize, sugarcane and coconut, roots arise from the base of the stem to give support. These are called **stilt roots** (Fig. 8.5.) 3 **Breathing Roots:** Mangrove plants (Fig. 8.6) grow in wet, salty areas in the coastal regions. Soil in such regions has very little oxygen. Thus, these plants have special roots, called **breathing roots** or **pneumatophores**. These breathing roots grow vertically upwards from the underground roots of the plants. They come out of the water in the shape of conical spikes. These roots have pores for exchange of gases. 4. **Climbing Roots:** Plants with weak stems such as betel, black pepper and money plant have special roots rising from their stem nodes. These roots help the plant to climb up any kind of support such as a wall, rock and tree (Fig 8.7.) 5. **Parasitic Roots:** Some plants such as dodder (Fig. 8.8.) that cannot make their own food have parasitic roots. These roots attach to other plants for obtaining nutrients and water from them. ### Modifications of Stems: In some plants, the stems are modified to perform special functions according to the needs of the plant. Some of the stem modifications are given below. 1. **Food Storage:** Stems in some plants such as ginger, potato and onion grow under the These underground stems are modified to store food. Common types of underground stems are **tubers** such as potato, **rhizomes** such as ginger and **bulbs** such as onion (Fig 8.10.) 2. **Provide Support:** Stems of climbers such as grapevine, cucumber, sweet pea and passion flower are modified into thread-like, spirally coiled structures. These structures are called **stem tendrils** (Fig 8.11) Tendrils wrap themselves around nearby objects and provide support to the plant. 3. **Storage of Water:** Plants that grow in deserts such as cacti have thick, fleshy stems (Fig. 8.12.) 4. **Manufacture of Food:** Stems of plants such as cactus become flattened. These flattened stems look like leaves and perform photosynthesis. 5. **For Protection:** Stems of plants such as rose (Fig 8. 13.) lemon, bougainvillea are modified into thorn-like structures to protect the pant from predators. ## Leaves: Leaves are of different shapes, sizes, colours and texture. Most plants have green leaves. Leaves prepare food for the plant. Parts of a leaf are shown in Fig 8.14. * The flat, green portion of the leaf is called the **leaf lamina** or **leaf blade**. Photosynthesis takes place in this part. * **Thin lines** that arise from midrib and run across the leaf in various directions are called the **veins**. These veins provide support to the leaf and transport water, minerals and food to and from the leaf to other parts of the plant. * A tube-like structure in the centre of the leaf is called the **midrib**. It extends from the petiole till the tip of the leaf. * Leaves are attached to the stem by a small stalk called **petiole** The arrangement of veins in a leaf is called **venation**. Two main types of venation seen in leaves are given below. * **Reticulate Venation:** In reticulate venation, the veins are arranged just like nets on both sides of the midrib (Fig 8.15). For example, peepal and mango. * **Parallel Venation:** In parallel venation, the veins run **parallel** to each other (Fig 8.16) For example, maize, wheat, coconut, grass and banana. ### Functions of a Leaf: Some of the functions of leaves are given below. * Leaves prepare food for the plant through a process called **photosynthesis**. So, leaves are called the **food factories** of the plant. * Leaves exchange gases through tiny pores called **stomata**. Stomata are present on the underside of the leaves. * Water comes out of the leaves in the form of water vapour through the stomata. This process of loss of water is called **transpiration**. ### Modification of Leaves: In some plants, leaves are modified to perform special functions. Some of the leaf modifications are given below. 1. **For Additional Support**: In some plants with weak stems, such as gloriosa lily and pea, the leaves are modified to form soft, coiled, wire-like structures called **leaf tendrils** (Fig. 8.17). Whenever the tendrils come in contact with an object, they coil around it. This provides additional support to the and helps the plant to climb up. 2. **Conservation of Water**: In some plants such as cactus, leaves are modified into sharp, pointed structures known as **spines**. They protect the plants from being eaten by animals. Spines also reduce the rate of transpiration. 3. **Trapping of Insects:** In some plants such as **pitcher plant**, leaves are modified to form pitcher-like structures for capturing insects (Fig. 8.18). These plants grow in regions where the soil is deficient in nitrogen. To overcome this deficiency, these plants have developed mechanisms to trap insects and absorb the nitrogen content from their bodies. These plants are also called **insectivorous** or **carnivorous plants**. However, they also prepare their own food through photosynthesis. ## Flowers: Flowers are the most distinctive and attractive parts of many plants. They are coloured, have pleasant fragrance and contain nectar to attract insects or animals. Flowers are the reproductive organs of flowering plants. A flower develops from a bud. It lives for a short time and then develops into a fruit. The fruit contains seeds which germinate into new plants when the conditions are suitable. ### Structure of a Flower: Parts of a flower are shown in Figure 8.19. * **Stamen:** The male reproductive part of a flower. It includes the filament and anther. * **Anther** is the head of the stamen that produces pollen grains. They are generally yellow in colour. * **Filament** is a long slender structure that supports the anther. * **Pistil:** The female reproductive part of a flower. It includes stigma, style and ovary. * **Stigma** is found at the tip of style and contains a sticky substance that holds onto the pollen grains during pollination. * **Style** is a long, thin, tube-like structure that holds the stigma * **Ovary** is the swollen base of the pistil that contains ovules (egg cells.) * **Petal:** The bright coloured part of a flower that protects the inner structures of the flower and attracts insects for pollination. * **Sepal:** It is the outermost layer of a flower that is green in colour. * **Pedicel:** The thin stalk by which a flower is attached to the stem or the branch of a plant. * **Thalamus:** It is the uppermost swollen part of the pedicel that bears the weight of a flower. ## Pollination: The transfer of pollen grains from the anther to the stigma is called **pollination**. It is aided by various pollinating agents such as insects, birds, wind and water. The flowers are brightly coloured or have a particular fragrance to attract insects. When insects sit on the flowers, the pollens stick to their body and legs. This gets dropped on other flowers when they move from one flower to the other, thereby facilitating pollination. Pollination is mainly of two types: self-pollination and cross-pollination. * **Self-pollination:** When pollen grains fall on the stigma of the same or another of the same plant, it is called self-pollination * **Cross-pollination:** When the pollens fall on the stigma of another on a different plant, it is called cross-pollination In most of the plants after pollination, the size of the ovary increases and it changes into the fruit. The ovules change into seeds. The sepals, petals and stamens fall off. The **fruit** consists of an outer covering called **pericarp** and a fleshy pulp which contains the seeds. Seeds develop into new plants when provided with sufficient air, water and sunlight.