Biology

Which part of the Plant is Responsible for Photosynthesis

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Which part of the Plant is Responsible for Photosynthesis

Leaves
Leaves are known as food factories of the plant. They arise from at the nodes of the stems and have a characteristic shape and size. Let us study its different parts.

Which part of the Plant is Responsible for Photosynthesis 1
Parts of a leaf

The arrangement of veins in a leaf is termed as venation. Venation is of two types: parallel and reticulate. If the veins run parallel to one another from the base to the tip of the leaf, the leaf is said to have parallel venation, e.g., banana and onion. If the veins are arranged in a net-like pattern on both sides of the midrib the leaf is said to have reticulate venation, e.g., peepal and mango.

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Parallel venation                        Reticulate venation

Functions of a leaf
A leaf performs various important functions for the plant.
It is usually green due to the presence of a green pigment called chlorophyll. A leaf prepares food for the plants. The process of making food by the plant using carbon dioxide, water, chlorophyll, and light is called photosynthesis.
Which part of the Plant is Responsible for Photosynthesis 3 Plants store food in the leaves, fruits, and stems in the form of starch.

  1. Plants breathe with the help of their leaves. Leaves of most plants have tiny openings called stomata under their surface.
    The exchange of gases takes place through the stomata.
  2. Leaves also lose water through the stomata. The loss of water through the stomata is called transpiration. Transpiration helps the plant in the following ways:
    • It helps in cooling the leaves, just as loss of water during sweating helps in keeping our bodies cool.
    • During transpiration, more water is ‘pulled’ upwards from the roots to compensate for the lost water. This water brings along important nutrients from the roots, which are required by the leaf. Thus, transpiration helps in the transport of nutrients within the plant.
    • Transpiration also plays an important role in water cycle.
      Which part of the Plant is Responsible for Photosynthesis 4
      Stomata

      Which part of the Plant is Responsible for Photosynthesis 5
      An open stomata

Leaf modifications

  • Leaves of some plants are modified to form special structures called tendrils. Tendrils help plants to attach themselves to a support. Plants having tendrils are generally climbers.
  • For protection, leaves of certain plants get modified to form spines. Spines also reduce the amount of water lost from the plant.

Activity
Aim: To observe transpiration in plants
Materials needed: A potted plant, water, and a polythene bag
Method:
1. Take a potted plant and water it.
2. Cover the plant with a polythene bag and keep it in a place that receives a lot of sunlight.
3. Observe the polythene bag after a couple of hours.
Observation: You will find tiny droplets of water on its inner surface.
Conclusion: These droplets are formed due to water being lost from the potted plant.
Water droplets are not seen when we ieave an empty plastic bag (with its mouth closed) outside. This suggests that plants transpire.

What Is Deforestation And Its Effects On The Environment

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Deforestation And Its Effects On The Environment

With the increase in human population, there have been ever-rising demands for converting forests into residential and agriculture areas. As a result, lots of trees are being felled and forests are being cleared, thus destroying the habitat of several species of animals and plants. Such large-scale felling of trees is called deforestation. It results in permanent destruction of forests and woodlands.

Forests are a valuable natural resource. Given below are some of the ways in which forests are beneficial to human beings and the environment.

  1. Forests provide habitat to a large number of plants, animals, birds, and insects.
  2. Trees release oxygen, which is needed for survival.
  3. We obtain useful products like timber, gum, paper, and medicines from forests.
  4. Roots of trees help to hold the soil in place, preventing soil erosion and landslides.
  5. Dead plants and trees decompose to form humus, which helps in maintaining soil fertility.

Deforestation refers to the continual degradation of forests due to natural or human-related causes. The main causes of deforestation are

  1. Requirement of wood,
  2. Rapid urbanization resulting in conversion of forests to agricultural land, and
  3. Overgrazing by cattle.

Deforestation may have many adverse effects. Some of them are:

  1. Soil erosion and desertification
  2. Destruction of the natural habitat of animals and birds: If forests are destroyed, global climate and local weather may change drastically. This will result in the loss of many species of animals and plants, and biological diversity.
  3. Large amounts of greenhouse gases such as carbon dioxide, methane, etc., are released into the atmosphere due to deforestation.
  4. Natural resources such as timber, medicinal plants, fruits, and nuts are depleted due to deforestation.
  5. Increase in global temperature
  6. Reduced rainfall
  7. Floods
  8. Landslides (in mountainous regions)

Case Study: Chipko Movement

The Chipko movement, launched in the early 1970s, aimed at preventing the cutting of trees in the Garhwal Himalayas.
The villagers hugged the trees and prevented the contractors from felling them. (The Hindi word ‘Chipko’ means ‘to embrace’ or ‘to hug’.)

What Is Deforestation And Its Effects On The Environment 1The success of the Chipko movement in the hills saved thousands of trees from being felled. Sunderlal Bahuguna, a Gandhian activist and philosopher, played an important role in success of this movement He appealed to Mrs Indira Gandhi, the then Prime Minister of India, which resulted in a 15-year ban on the felling of trees in the Himalayan forests.

Here are some practices that could help in conserving our forests.

  1. Trees should be planted on a large scale on available land. Large-scale planting of saplings is called afforestation. When this is done on deforested lands, it is called reforestation.
  2. More forest reserves and botanical gardens should be established.
  3. Allowing animals to graze on the same patch of land for a long period of time should be avoided. Minimizing overgrazing by animals will go a long way in preventing farmlands from turning barren.
  4. Measures should be taken to prevent and control forest fires.
  5. Awareness programmes could be conducted by school children, organizations, and also through print and television advertisements to promote the need to use our forest resources judiciously.
  6. Since paper is obtained from wood pulp, recycling of paper will also help conserve trees to some extent.

What is Viviparous Reproduction

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What is Viviparous Reproduction

Viviparous and Oviparous Animals

Based on how they produce offspring, animals can be divided into the following two types.
Viviparous animals:
Animals that give birth to live offspring (i.e., babies) are called viviparous animals. Mammals like cow, horse, dog, cat, and human beings are examples of viviparous animals.

Oviparous animals:
Animals that lay eggs, which hatch into offspring, are called oviparous animals. Birds, snakes, frogs, and butterflies are examples of oviparous animals.

Newly hatched birds and young ones of mammals look similar to their parents. However, in some animals the newly hatched individuals do not resemble the parents and undergo a series of changes (called metamorphosis) after birth. Let us understand this process using the life cycles of frog and butterfly.

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Metamorphosis in Frog and Butterfly

There are three main stages in the life cycle of a frog:

Egg —-► Larva (tadpole) —-► Adult

The various changes that occur during the life cycle of a frog are shown in Figure.
What is Viviparous Reproduction 1
These changes are controlled by the hormone thyroxine.
Similarly, there are four main stages in the life cycle of a butterfly:

Egg —-► Larva (caterpillar) —-► Pupa —-► Adult

The changes that occur during these stages are controlled by two hormones: juvenile hormone and ecdysone. The larva transforms into an adult after undergoing a series of drastic changes. The transformation of a larva into an adult through a series of drastic changes is called metamorphosis.

Cloning is a technique through which multiple copies of a single gene, chromosome, or whole organism can be produced. Perhaps the most famous example of cloning is Dolly the sheep, which was cloned at Roslin Institute, Scotland. Cloning has many applications, including generation of tissues and organs for transplant.

What Determines the Gender of the Child

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What Determines the Gender of the Child

Determination of the Sex of a Baby

Do you know what determines whether the baby developing inside the mother’s womb is a boy or a girl? This is determined by chromosomes, the thread-like structures found inside the nucleus. Chromosomes carry information in the form of genes. Each cell contains 23 pairs of chromosomes, including one pair of sex chromosomes. There are two types of sex chromosomes, X and Y, named after their shapes. Female cells contain the XX pair while male cells have the XY pair.

The gametes (sperm and ovum) contain only one set of chromosomes consisting of one member of each pair. Ovum contains one X chromosome while a sperm may contain either of the two sex chromosomes—X or Y. When the ovum gets fertilized, the sex of the baby will depend on which sperm fertilizes it. If a sperm carrying the X chromosome fertilizes the ovum, the baby will be a girl, as the chromosome pair will be XX. If a sperm carrying the Y , chromosome fertilizes the ovum, the baby will be a boy, as the chromosome pair will be XY.

What Determines the Gender of the Child 1

Baby Inside the Womb

When the fertilized egg reaches the uterus, it implants itself there. During the first eight weeks after fertilization, the baby is called the embryo. From eight weeks after fertilization till birth, the developing baby is called the foetus. The baby stays and grows inside the mother’s womb (uterus) for about 40 weeks to develop fully. When the foetus is fully developed, the mother gives birth to the baby.

What Determines the Gender of the Child 2
Baby inside the womb

Care After Birth

A newborn baby is very small and is unable to look after itself. The mother nurses the baby on her milk, which helps it to grow and develop resistance to diseases. A newborn baby depends on people around it for all basic needs and, therefore, requires a lot of care. A baby also needs to be vaccinated against diseases right from birth.

Gender issues and myths

Even though we are living in the 21st century, some people still consider the female child to be a burden. Techniques like ultrasound, which enable doctors to determine the sex of the unborn child, are being misused by such people for killing the girl foetus using a technique called abortion. To put a stop to female infanticide (killing of girl foetus), the government has made it illegal to find out the sex of the foetus. Even then, issues like lack of basic education for girls and early marriage and motherhood continue to persist, especially in developing countries.
Many people blame the mother for the birth of a girl child. Such thinking is scientifically baseless. As we discussed earlier, the sex of a child is determined by the father’s sperm (which carries either the X chromosome or the Y chromosome). Many such gender myths continue to be prevalent. These can only be dispelled by providing basic education to people.

Problems of adolescent pregnancy

Each year, about 16 million children are born to girls in the 15-19 year age group worldwide.
Since girls are not physically and mentally prepared for motherhood at such an early age, adolescent pregnancy is dangerous to both the mother and the child. Besides posing health problems, early marriage and motherhood also restrict educational opportunities for girls.

What is Reproduction in Humans

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What is Reproduction in Humans

Reproduction in Human Beings

In human beings and almost all mammals, the reproductive systems in males and females are different, with different organs performing specific functions. Before we learn about the male and female reproductive organs in detail, let us understand the basic process of reproduction.
Both males and females have special reproductive cells called gametes. The female gamete is usually called an ovum (or egg) and the male gamete is called a sperm.

What is Reproduction in Humans 1
Ovum                                                                                                                                      Human sperm

The two gametes join or fuse during a process called fertilization. This initiates the formation of a baby. An overview of the different stages of reproduction in human beings is given below.
What is Reproduction in Humans 2

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Male and Female Reproductive Organs

Let us now understand the structure and the functions of male and female reproductive organs.

What is Reproduction in Humans 3

What is Reproduction in Humans 4

Fertilization

The fusion of male and female gametes to produce a new organism is called fertilization. The main
stages of fertilization in human beings are listed below.

  1. Once a month, an ovum is released from the ovary by a process called ovulation.
  2. The ovum moves into the oviduct (fallopian tube).
  3. During sexual intercourse, the male transfers sperms in the vagina through the penis. The sperms travel through a narrow opening called cervix into the uterus and then the oviduct.
  4. A single sperm fuses with the ovum in the oviduct and fertilization takes place. The fertilized ovum continues its journey down the oviduct, into the uterus.
  5. The fertilized ovum implants itself into the uterus wall and develops into a human embryo.

This process is summarized in Figure

What is Reproduction in Humans 5

There are two types of fertilization: internal and external.

  1. Internal fertilization: In this type of fertilization, the fusion of male and female gametes occurs inside the female’s body. Mammals like cow, horse, dog, cat, and human beings are examples of organisms that reproduce by internal fertilization.
  2. External fertilization: In this type of fertilization, the fusion of male and female gametes occurs outside the body. Fish, frog, and starfish are examples of organisms that reproduce by external fertilization.

In vitro fertilization (IVF) is a technique in which the sperm and ova are combined in a laboratory dish. After fertilization, the embryo is transferred into the woman’s uterus. Babies conceived through this technique are called test tube babies.

Activity

Aim: To observe a fertilized egg of a hen
Materials needed: Some farm eggs and a torchlight
Method: Place a few farm eggs in a dark room and, using a torchlight, try to observe which of them show a tiny blood vein (reddish in colour) through the yolk. You may need to examine quite a few to find a fertilized egg.
Observation: A fertilized egg will show a tiny blood vein (reddish in colour) through the yolk.
Note: Handle the eggs carefully so as not to disturb the babies developing inside.