Plant Physiology: Definition, Regulation, Experiments

What Is Plant Physiology?

Plant physiology is the science of functions and vital processes of plants, how they live, grow, and respond to environmental factors. Knowledge in plant physiology applies to improved farm practice and management of plant health, as well as in advancing biotechnology.

The basic physiological processes are photosynthesis—the conversion of light energy into chemical energy; respiration, releasing the energy in organic molecules; transpiration, the process of water movement through plants and its evaporation from the aerial parts; and nutrient uptake, including the absorption of the essential minerals from the soil. All of these are major processes for growth, development, and survival in plants.

Plant Cells And Tissues

Plant cells are made with a stiff cell wall of cellulose, one large central vacuole, and chloroplasts inside which photosynthesis occurs.

Structure Of Plant Cells

The other organelles making up the plant cell nucleus are the endoplasmic reticulum, Golgi apparatus, mitochondria, and plasmodesmata.

Types Of Plant Tissues

The different types of plant tissue are:

Meristematic tissue

• It takes place in regions of the plant that are experiencing cell division, e.g. at the tips of roots and shoots.

• It is associated with a higher rate of growth and development in a plant.

Permanent tissue

• Differentiated from meristematic tissue cells that have stopped dividing.

• Being composed of simple tissues like parenchyma, collenchyma, and sclerenchyma, together with complex tissues like xylem and phloem

Physiology Of Plant Parts

The physiology of the plant parts is described below:

Leaves – Photosynthetic Organs

The primary photosynthetic organs that produce food through the conversion of light energy into chemical energy

Contain chloroplasts with the green pigment, chlorophyll, which captures light energy

The surface of the leaf has a small opening, known as the stomata, which regulates gas exchange and the loss of water in a plant into the atmosphere through the process of transpiration.

Stem – Support and Conduction

• Holds up the plant to keep leaves extended into their rightful position to receive sunlight.

• Stems transport water, nutrients and sugars produced from photosynthesis from roots to leaves.

Roots – Absorption and Anchorage

• Anchor the plant in the soil and help absorb water and nutrients.

• Their surface area is increased by root hairs for better absorption.

• They store food and nutrients in some plants.

Xylem and Phloem – Transport Tissues

There are two major transport tissues, xylem and phloem.

Xylem

• Xylem transports water and dissolved minerals from the root to other parts of a plant.

• It consists of vessels, tracheids and supportive fibres.

Phloem

• Transport organic nutrients, mainly the sugars that are produced via photosynthesis from leaves to other parts of a plant.

• This tissue includes a siege tube, companion cells, phloem fibres, and phloem parenchyma.

Photosynthesis in Plants

Photosynthesis is a process whereby cells convert glucose and oxygen into energy, carbon dioxide, and water. This is the way it derives its energy for cellular work.

Role Of Chlorophyll And Other Pigments

Chlorophyll:

• Chlorophyll is the major pigment involved in photosynthesis. It shows maximum absorption in the blue and red parts of visible light. End

• A green pigment located in the chloroplasts; it captures light energy, which is then used to convert carbon dioxide and water into glucose and oxygen.

Other Pigments:

• Carotenoids are yellow, orange, and brown pigments that absorb light at various wavelengths, thus protecting the photosynthetic apparatus from photo damage, and extending the range of light that the photosynthetic apparatus can use.

• Anthocyanins absorb light in the UV region of the spectrum and take part in the attraction of pollinators.

Basic Steps of Photosynthesis

Photosynthesis occurs in two fundamental stages: light-dependent reactions and light-independent reactions or Calvin Cycle. The two stages collaboratively engage in converting light energy into the chemical energy housed within glucose.

Respiration In Plants

Respiration in plants occurs by the following two means.

Aerobic Respiration

Aerobic respiration is a method of respiration carried out in the presence of oxygen where glucose is completely oxidized into carbon dioxide and water with the production of a large amount of ATP as energy.

Process: Breakdown of glucose in the mitochondria through several different pathways that involve first of all the citric acid cycle and then oxidative phosphorylation.

Anaerobic Respiration

The process of respiration without oxygen: glucose is broken down partially to form less energy with by-products such as ethanol or lactic acid.

Process: Glucose turns into pyruvate using glycolysis and then, via reduction, into ethanol and carbon dioxide in yeast, or it is reduced to lactic acid in some plant tissues.

Factors Affecting Respiration

• Availability of Oxygen: Enough quantities of oxygen are needed for proper aerobic respiration.

• Temperature: Respiration increases upon an increase in temperature to a point beyond which further increase in temperature may be associated with falling rates of respiration.

• Availability of Water: This component is required not only for the activation of most enzymes but also in the stages of cellular respiration.

• Glucose Concentration: The increase in glucose levels gives a corresponding increase in respiration rates, as more fuels would then be available.

• Light intensity increases the rate of transpiration; temperature—with increasing temperatures, increasing transpiration; humidity—the rate of transpiration increases with decreasing relative humidity of the air; wind—increases the rate of transpiration due to blowing away water vapour from the surfaces of the leaves.

Water and Mineral Absorption in Plants

There are various means of transport in plants.

Role of Root Hairs

These root hairs increase the surface area of roots and thereby increase the amount of water and minerals absorbed from the soil. They increase the uptake of essential nutrient ions and water through osmosis and active transport.

Water Ingestion

The water moves from high potential in the soil to an area of low potential in root cells through the process of osmosis.

Mineral Ingestion

Minerals are taken up by the root cells from the solution of the soil through mechanisms of active transport

Transpiration and Its Regulation

Transpiration is the process through which plants absorb water from the soil using roots, transport it through the plant, and then give out the water into the atmosphere through the stomata in the leaves. This helps cool the plant, provides turgor pressure, and promotes nutrient uptake.

Factors affecting transpiration

Factors that influence transpiration include light intensity, which increases the same, temperature, whereby high temperatures increase the same, humidity with low humidity increasing the same and wind, which increases the same through the removal of water vapor from the surface of the leaves.

Translocation Of Nutrients

Translocation of nutrients is performed by xylem and phloem.

Role of Xylem

Xylem is the tissue responsible for absorbing water, along with dissolved minerals, from roots and carrying it to all parts of the plants. This tissue works because of capillary action itself and creates negative pressure by the process of transpiration.

Role of Phloem

Phloem is the conducting tissue transporting the photosynthetic products—primarily the sugars—on its flow from the leaves, its source, to the other parts of the plant where use or storage takes place. Active mechanisms of transport are coupled with this pressure flow in such a process.

Plant Physiology NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Photosynthesis in Plants

• Respiration in Plants

Practice Questions for NEET

Q1. The Father of Indian plant physiology is

1. Satyendra Nath Bose

2. Meghnad Saha

3. Jagdish Chandra Bose

4. Srinivas Ramaujan

Correct answer: 3) Jagdish Chandra Bose

Explanation:

The study of various plant functions and processes, namely growth, development, photosynthesis, and nutrient uptake, will be covered under the term 'plant physiology.' Stephan Hales was known as the father of plant physiology due to his fundamental experiments on plant fluids. J.C. Bose is known as the father of Indian plant physiology for the research on the response and signalling mechanism through plants by the latter, which contributed much to the field.

Hence the correct answer is Option 3. Jagdish Chandra Bose

Q2. Which of the following was proposed by the Father of Indian Plant Physiology?

1. Vital theory

2. Root pressure theory

3. Physical force theory

4. Transpiration pull theory

Correct answer: 1) Vital theory

Explanation:

The Pulsation Theory supporting the vital theory was given by J.C Bose. It proposed pulsation activity in the innermost cortical cells which is responsible for the ascent of sap.

The Father of Indian Plant Physiology- J.C. Bose (Jagadish Chandra Bose),- put forward the Vital Theory. He challenged the conventional wisdom that plants were passive entities by advancing our understanding of plant physiology and putting forth the theory that plants share essential life activities with animals. His research opened the door for more studies on the communication and behaviour of plants.

Hence, the correct answer is option 1)Vital Theory.

Q3. Directions: In the following questions, a statement of Assertion (A) is followed by a statement of reason (R).

Assertion: The buttercup plant produces two different types of leaves within the same plant body.

Reason: Plasticity enables Buttercup to follow different pathways in response to environmental changes.

Mark the correct choice as:

1. If both assertion and reason are true and reason is the correct explanation of assertion

2. If both assertion and reason are true but reason is not the correct explanation of assertion

3. If assertion is true but reason is false

4. If both assertion and reason are false

Correct answer: 1) If both assertion and reason are true and reason is the correct explanation of assertion

Explanation:

The ability of a plant to adapt to its surroundings by altering its growth, development, and metabolism is known as plant plasticity. This enables plants to endure adverse circumstances and adjust to swift changes in their surroundings.
Here are a few instances of plant plasticity:
Heterophylly cotton
An illustration of the flexibility of plants
The coriander
When coriander plants are young, their leaves have a different shape than when they are grown.
Buttercup
When buttercup plants are grown in air as opposed to water, their leaves take on a distinctive shape.

Hence, the correct answer is Option (1) If both assertion and reason are true and the reason is the correct explanation of the assertion.

Also Read:

• MCQs on Plant Physiology

• Light Dependent Reactions

• Glycolysis

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