Before starting with Class 7 Science Chapter 1 i.e. ‘Nutrition in Plants’, I am hoping that you have completed the 6th class. If not, then you can go through its Notes and NCERT Exercise Solutions whose links have been provided below. ⤵️
Table of Content
Introduction
In the previous class, we learnt that plants prepare their food and animals directly or indirectly depend upon the plants for their nutrition, other than that we have also learned about the components of food i.e. carbohydrates, fats, protein, water, minerals, roughage or fibres etc.
Nutrition and Its Modes
Nutrition encompasses the mode by which an organism takes up food and its utilisation in the body.
The basic functions of food are:
- provide energy to our body to work properly.
- promote the growth of our body.
- repair the damaged body parts, etc.
Broadly there are mainly two different modes of nutrition that exist in nature.
1. Autotrophic Mode of Nutrition
Auto = Self
Trophos = Nourishment
In this mode of nutrition, organisms prepare or make their food from simple substances.
Photosynthesis is an autotrophic mode of nutrition.
Organisms that have an autotrophic mode of nutrition are called autotrophs. e.g. green plants are autotrophs.
2. Heterotrophic Mode of Nutrition
Heteros = Others
Trophos = Nourishment
In this mode of nutrition, organisms get their nutrition or food from other organisms rather than preparing it themselves.
Organisms that have a heterotrophic mode of nutrition are called heterotrophs. e.g. human beings are heterotrophs.
Photosynthesis: Food-Making Process in Plants
Photo = Light
Synthesis = To combine
Photosynthesis is a process by which plants prepare their food by using carbon dioxide from air, water and minerals from the soil in the presence of sunlight and chlorophyll.
Leaves are the food factories of plants.
How Carbon Dioxide is Taken in by the Plants?
Plant leaves have very tiny pores on them known as stomata which are guarded by guard cells. Through these pores, the plants take in carbon dioxide and release oxygen.
How Water and Minerals are Transported to Leaves?
Plants have a network of fine vessels that run like pipes throughout the root, the stem, the branches and the leaves.
Vessels form a continuous path for water and minerals to reach to the leaves.
Chlorophyll
It is a green-coloured pigment that is present in green parts of a plant and it is responsible for capturing the energy of the sunlight, later this energy is used to carry out the process of photosynthesis.
The solar energy is captured by the leaves and stored in the form of food in a plant. Thus, the Sun is the ultimate source of energy for all living creatures on Earth.
Besides leaves, chlorophyll is also present in the green stem and it also performs the process of photosynthesis just like leaves.
Some plants have leaves of different colour but that doesn’t mean they don’t have chlorophyll in them. Actually, in those plants, the green colour of chlorophyll is masked by other coloured pigments like carotene and xanthophyll, etc. imparting a different colour to the leaves.
So, the main components of photosynthesis are:
- Carbon dioxide
- Water
- Chlorophyll
- Sunlight
Did you know:
The slimy green patches of algae that we see on water bodies are actually plants and they perform photosynthesis just like trees.
Equation of Photosynthesis
Excess of food is stored by a plant in the form of starch. whose presence can easily be tested by the iodine test.
Synthesis of plant food other than carbohydrates
Only carbohydrates are synthesized by the process of photosynthesis. Plants also synthesize other macronutrients such as fats and proteins.
For protein synthesis plants need glucose and nitrates (water-soluble form of nitrogen).
Nitrogen is present in abundance in our atmosphere but plants can’t absorb this nitrogen directly. So, this atmospheric nitrogen has to be first converted into a different form that can be easily absorbed by a plant and this can be done by various nitrogen-fixing bacteria, e.g. Rhizobium, Azotobacter, etc.
Cells
Just like buildings are made up of bricks, bodies of living organisms are also made up of tiny structural and functional units called cells. Most of them are visible under a microscope but some of them can be seen with naked eyes.
Some organisms are only made up of one cell called unicellular organisms. In contrast, some are made up of more than one cell called multicellular organisms.
Each cell is enclosed by a thin outer layer or boundary called the plasma membrane.
Most of the cells have a distinct, centrally located spherical structure called the nucleus.
The cell is filled with a jelly-like substance called the cytoplasm or cytosol.
Other Modes of Nutrition in Plants
Not all plants are autotrophic in nature, some of them are heterotrophic in nature as well.
1. Parasitic Mode of Nutrition
Some plants like Cuscuta (Amarbel) lack chlorophyll. So, they can’t prepare their food and hence they are dependent upon other plants for their nutrition.
Cuscuta climbs up its host tree and sucks its readymade food via special roots called haustorial roots. And slowly slowly the host plant starts to get weaker and dies out.
2. Insectivorous (Insect Eating) Plants
These plants are green in colour and they do perform photosynthesis, yet they are heterotrophic in nature. This has to do with the location they grow in. Most of insectivorous plants grow in soil that lacks nitrogen, so they consume animals (insects) to fulfil their nitrogen requirements.
Insectivorous plants are partially heterotrophic.
3. Saprotrophs
You have seen the mushrooms and bread molds growing in damp and dry weather conditions. Well, those aren’t technically plants, they are fungi. But, they are saprotrophic in nature.
Saprotrophic nutrition is a mode of nutrition in which organisms directly take nutrients from the dead and decaying matter.
Some plant(s) like Indian pipe also known as ghost plant is an example of saprotrophs.
Other than plants, most of the fungi are saptrophic in nature. Fungal spores are present in air and when they land on a dry the wet and warm things they start to germinate and grow.
Fungi are a very weird organims. Some of them are beneficial for us and some of them are really dangerous for us.
For example:
- They cause diseases in plant crops, e.g. wheat rust and wheat smut, etc.
- They cause diseases in animals as well, e.g. skin infections, etc.
- They are edible as well, e.g. mushrooms.
- Yeast (which is a fungus) is used in bread making and fermentation.
- They are also used for making medicines, e.g. anibacterial medicines (penicillin), etc.
Did You Know?
The Irish potato famine was caused by the destruction of potato crop by a fungus. About a million people lost their lives due to this famine.
How Nutrients are Replenished in the Soil?
Have you ever seen farmers spreading compost, manure or fertilizers in their fields?
Have you ever wondered, why do they do this?
We know that plants absorb minerals from the soil. So with cropping the nutrient amount in soil decreases. So, to ensure that the crops keep on getting the important nutrients, we need to replenish or refuel the soil with nutrients and this can be done by various means. By
- Using manure (made up of animal excreta)
- Using compost (from the decomposed plant material and organic matter) or Vermicompost as well.
- Using fertilizers (factory-made chemicals like NPK- nitrogen, phosphorus and potassium mixture, urea, etc.)
- Using biofertilizers (organisms that replenish the used nutrients, e.g. Rhizobium bacteria for leguminous crops like pulses, it replenishes the nitrogen in the soil).
Symbiotic Relationship
In this type of relationship, organisms live together and share both shelter and nutrients.
Examples of some of the most common symbiotic relationships are:
- Some fungi live inside the roots of plants. The plant provides food to the fungi and fungi help it in absorbing water and nutrients.
- Lichen: is a symbiotic relationship between chlorophyll-containing algae and a fungus. Algae provide food to the fungi and fungi provide shelter, water and nutrients to the algae.
3. Rhizobium bacteria and the leguminous plants. Rhizobium provides the plant with soluble nitrates and in return the plant provides food to the Rhizobium. This relationship can be very useful for farmers as it can save them from costly and soil-eroding fertilizers.
Conclusion
We all can learn from the symbiotic relationship among various organisms about the concept of co-existence in peace.
References & Credits
- Class 7th Science NCERT Textbook
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