Plants

Sexual reproduction in plants.

We have learned in previous articles about asexual reproduction in plants. We shall learn about sexual reproduction in plants.

What do you know about sexual reproduction in plants?

Plants reproduce sexually for the same reasons as any other organism- to maintain genetic diversity. Sexual reproduction in plants is limited to flowering plants. Flowering plants are those plants that produce flowers. Have you ever wondered why flowers are so colourful or smell so good?

Plants invest a lot of energy in producing flowers. The flowers are bright to attract insects and bees. These insects and bees transport the pollen from one flower to another, thus, helping with the process of sexual reproduction in plants.

Flowers have only one role- sexual reproduction in plants. We have studied about the parts of a flower previously. Can you recollect the parts of a flower?

sexual reproduction in plants

Flowers are composed of sepals, petals, stamens and carpels. The sepals and petals protect the stamens and carpels. The stamens and carpels are the reproductive organs of the plant. The stamens are the male reproductive organs and the carpel is the female reproductive organ of a plant.

Plants are of two types- unisexual and bisexual.

Unisexual Plants– These plants have flowers that comprise only of stamens or carpels. Examples include papaya and watermelon. Therefore, these plants can only be fertilised by pollen from another plant.

Bisexual plants- Flowers of these plants contain both stamens and carpels. Thus, these plants can be fertilised by pollen from the same plant or another plant. Examples include Hibiscus and mustard.

sexual reproduction in plants

Stamens produce pollen. Pollen is the sticky, yellow powder that sticks to our hands if we touch it. The powder corresponds to the male gamete of the plant. When bees and other insects come in contact with the pollen, the pollen sticks to their feet and are transported to other flowers. This process is called pollination. Bees play a critical role in pollination. We will discuss the role of bees in agriculture in another article.

The carpel is the female reproductive organ of the plant. The carpel comprises of the ovary, the style and the stigma. The ovary is the bottom, swollen part of the carpel. The style is an elongated tube that functions to transport the pollen and the stigma is the sticky top part of the carpel. Pollen is deposited on the stigma and it travels through the style to reach the ovary. Here, it fuses with the female gamete to produce seeds. Once a flower is pollinated, the rest of the parts of the flower shrivel and fall off.

There are two terms one usually comes across about pollination:-

Self-pollination- Pollen from the same plant fertilise the ovule.

Cross-pollination– Pollen from another plant fertilises the ovule.

To summarise, sexual reproduction in plants is vital for maintaining genetic diversity and forms the basis of most agricultural innovation. Flowers are the reproductive organs of the plants and these flowers can either be fertilised by pollen from the same plant or another plant.

Click here for more biology notes.

Here is an outstanding collection of CBSE books to help you prepare for your board exams.

Movement in Plants

We have all seen trees swaying in the wind. Is it an example of movement in plants? In the strictest sense, yes. However, this action is not indicative of life. Even a dead tree or plant can sway in the wind. The movement of plants here is caused by the wind and is not intrinsic to the tree or plant. So, what movements are essential to a tree or plant?

There are two such movements in plants that are indicative of life. One is the immediate response to stimuli and the other is in response to growth.

Prof. Jagdish Chandra Bose, an Indian physician, biologist and scientist was the first to demonstrate movement in plants. He invented the crescograph, an instrument that can be used to measure movement in plants.

Have you seen or touched the ?touch-me-not? plant (Mimosa pudica)? As soon as you reach the leaves, they droop and curl up. How does this happen?

Plants do not have specialised structures like nerves or neurones to control their movement. They instead rely on electromechanical signals to control movement in plants. In the above example, when we touch the leaves, the leaves sense the pressure, and this is transmitted as electric signals to the cells adjoining the leaves. These then quickly lose water, leading to drooping of the leaves. In fact, most of the movement in plants is due to ingress and egress of water from the cells.

Another movement in plants is in response to growth. We have all eaten sprouts. Have you noted how your mother makes these? Sprouts are made from a class of plants called lentils. There are different varieties of lentils, and the seeds of these plants are soaked and allowed to germinate to produce the sprouts.

When these seeds are soaked in water and left in air, they germinate, and you can see the roots and shoots coming out. If you leave them long enough, one can see them grow in length. This movement in plants is a manifestation of growth. If we take this germinating seed and plant it in the soil, in a few days you will note that the shoot starts growing upwards, and a new plant is born.

What would happen if we suspend this germinating seed in the air? Will the root grow upwards or the shoot grow downwards? ?No, irrespective of where a seed is planted, the roots will always grow in the direction of gravity, and the shoots will grow against gravity.

Now let us set up another experiment. Take two potted plants and keep them inside a cardboard box. In one box, make a hole on one side to let in sunlight. Maintain the plants for a few days inside these boxes. What would you notice?

You would see that the plant in the box with the hole has grown in the direction of the hole. Movement is plants in influenced by the direction of sunlight. Gravity also affects movement in plants. This movement in plants is called as tropism or more accurately called heliotropism and geotropism respectively.

Plants can also move in response to chemical stimuli. In the above experiment, the plant grows in the direction of sunlight by the action of a chemical called Auxin. This chemical diffuses to the shady side of the shoot and stimulates growth on that side. Therefore, the shoots grow towards the sunlight.

Thus, we have learnt that movement in plants can be a manifestation of growth, or it can be in response to environmental changes. Even though plants do not have a nervous system, they can move using electromechanical or chemical signals.

Click here for more class 10 science notes.

Life Processes: Transportation in Plants

Transportation in plants is an important life process. In our previous articles on life processes, we learnt that plants utilise water and carbon dioxide to produce oxygen and energy in the form of starch. The water and other nutrients like nitrogen and phosphorus are present in the soil and plants absorb these from the soil. Plants have specialised tissue called roots that perform this function. The roots of the plants not only anchor the plant to earth, they also have fine fibrils that increase the surface area available for absorption of water and nutrients manifold.

Once water and other nutrients are absorbed, they need to be transported to the leaves, where the actual process of photosynthesis happens. In small plants, transportation of water and nutrients can happen by diffusion. However, diffusion is unsuitable for moving water and nutrients across large distances, especially in very tall trees. Therefore, trees have a well-developed system of transportation- namely the xylem and phloem. The xylem is a specialised system of transportation in plants that helps move water and nutrients absorbed from the roots to the leaves. There are two processes going on here, firstly the salt ions absorbed by the roots create a concentration gradient. This concentration gradient helps in the movement of water across the cell membranes. Secondly, the stomata in the leaves lose water by a process called as transpiration. Transpiration creates a negative suction pressure that helps move the water and other nutrients through the xylem. This system is quite similar to a wick. Have you ever noted that if you dip one of a wick in water or oil, in a matter of few minutes, the water or oil will slowly move across the whole length of the wick? This process is called the capillary action. Thus, transportation in plants is dependent on diffusion, capillary action of the transportation systems and also transpiration. Together, these processes can transport many litres of water from the soil to the leaves in any day. During the night, this process does not stop but continues at a slower rate as transpiration is shut down.

Similarly, substances like glucose, amino acids and fatty acids move from the leaves to storage organs like roots, fruits and seeds. The phloem is a specialised tissue that transports these substances from the leaves to other parts of the plants. Unlike the xylem, transportation through the phloem is driven by energy. Therefore, this is an active process and can proceed even against a concentration gradient. Plants use the energy stored ATP bonds to accomplish this task.

Thus, we have learnt that transportation in plants is a specialised process by which plants transport water and other nutrients to the leaves and then transport the finished products to their organs of storage. The Xylem and Phloem are specialised systems that perform this task. Students of class 10 science should be familiar with the process of transportation in plants as this is an important topic.

Click here for CBSE books that make this topic easy to understand.

The Starch Test: Experiments for class 10 science

Students are often asked to perform a starch test in class 10 science. What is a starch test and what is the aim of this test? We shall learn more about this in this article.

All class 10 science students should perform this experiment at least once. This is very easy and fun to perform and students will find this way of learning science very innovative. The aim of the starch test is to demonstrate the presence of starch in leaves after exposure to sunlight.

Starch is a form of complex carbohydrate. Plants store the chemical energy in the form of starch. In this test, we will try to demonstrate this fact.

Items required

A potted plant with variegated leaf, like money plant

A beaker of boiling water

A beaker of alcohol

Water bath

Bunsen burner or any other source to heat the water bath

Dilute solution of iodine

Tracing paper

Method

  • Take a potted plant and keep in dark for 3-4 days. This will allow the plant to use all the stored starch.
  • Then keep the plant in sunlight for 4-6 hours.
  • Pluck one leaf from the plant, preferably with many green areas.
  • Trace the outline of the green areas on a tracing paper.
  • Dip the leaf in boiling water for 1 minute.
  • Then dip in a beaker of alcohol and warm the alcohol mixture in a water bath. Wait for the alcohol to boil. What do you note?
  • You will note that the leaf loses its green colour and the alcohol becomes green in colour. Chlorophyll, the green pigment in leaves is soluble in alcohol. When dipped in alcohol, this pigment dissolves leading to the green discolouration of alcohol.
  • Now remove the leaf, wash with plain water and dip in a solution of iodine. What do you see?
  • You will note that a few areas of the leaf turn blue in colour.
  • Now compare these areas with the trace of the leaf. You will note that these blue areas correspond to the green areas of the leaf.

Explanation

This above experiment is based on a simple chemical reaction. Iodine reacts with starch to produce a blue colour. The green areas of the leaf contain chlorophyll. This pigment uses the energy of sunlight to produce carbohydrates from water and carbon dioxide. Starch is the commonest form of carbohydrate produced by plants. When exposed to sunlight, the green areas produce starch. This starch reacts with the iodine to form a blue colour, this corresponds to the green areas of the leaf.

This experiment demonstrates the importance of chlorophyll in photosynthesis. This experiment also demonstrates that chlorophyll is soluble in alcohol and that it is green in colour, thus accounting for the green colour of plants.

Click this link for more articles on class 10 science.

Click here for CBSE books.

Understanding Nutrition: A primer for class 10 science

A class 10 science student is expected to know about nutrition in detail. In our previous article on life processes, the concept of nutrition was introduced to students. In this article, we shall build on those concepts.

Living beings need energy to function. This energy is either produced by self by using elements available in the environment or is obtained from other living beings. The former are called autotrophs and the later heterotrophs. Plants and some single-celled organisms like bacteria, plankton, algae and protozoa belong to the former category.

Autotrophic nutrition

The concept of photosynthesis has previously been introduced to class 10 science students. This is the process by which plants use the energy from sunlight to produce and store energy. In addition to sunlight, plants also use water and carbon dioxide (all energy sources on earth are carbon based, at least in the living world).

Have you ever wondered why plants look green? Plants contain a pigment called chlorophyll, which converts the energy in sunlight to chemical energy which is then stored in the form of carbohydrates. ?This process can be represented in the following chemical equation:

6CO2 + 6H2O ==========???? C6H12O6 (Glucose)? + 6 O2

?????????????????????????????????????????????? Sunlight ? ? ? ? ? ? ? ?

?????????????????????????????????????????????? Chlorophyll

Plants obtain water from the soil. Some plants are capable of absorbing water from the ambient air as well. Plants have a well-developed system to transport this water to the leaves where it is converted to carbohydrates. Water is absorbed from the roots, then transported along the xylem. Carbon dioxide is absorbed from through the leaves. Leaves contain pores called as stomata. These pores are guarded by guard cells. The opening and closing of pores is based on the absorption of water by these guard cells. When guard cells absorb water, they swell up and open the pores. When they lose water, they shrink and pores close. By this mechanism, plants also reduce the loss of water from the leaf surface (transpiration). In the leaf, chlorophyll uses the energy of sunlight to combine water and carbon dioxide to carbohydrate. The excess carbohydrates are stored by the plants as starch which is what provides energy to animals and other living beings which depend on plants for their nutrition.

In addition to water and carbon dioxide, plants also require other elements. Nitrogen is required for synthesis of proteins and other compounds. Other minerals like potassium and phosphorus are also required. These elements are also absorbed from the soil through the roots of the plant.

To summarise, heterotrophs are those living beings which can synthesise energy from elements available in the environment and sunlight. They produce and store energy in the form of carbohydrates (in some cases fat). Heterotrophic organisms are dependent on autotrophs, either directly or indirectly for their nutrition.

Click this link for more articles on class 10 science.

Click here for CBSE books.