Life Processes in Plants

A Visual Quick Reference Guide to Growth, Photosynthesis, Transpiration, and Plant Respiration.

10.1 Plant Growth Requirements

Observations

Plants increase in size, height, and weight throughout their life span. Growth relies heavily on environmental inputs tested across pots:

Direct Sunlight + Regular Water

→ Healthy growth, lush green leaves.

Direct Sunlight + No Water

→ Plant wilts and dies rapidly.

Dark Room + Regular Water

→ Poor, pale, stunted growth.

Inference:

"Plants require both sunlight and water to synthesize food and sustain cell division."

10.2 Photosynthesis

Food Factory

Leaves are the "food factories" of plants. They contain chlorophyll, a green pigment that traps sunlight energy to convert simple compounds into chemical energy.

The Word Equation

Carbon Dioxide + Water
—(Sunlight / Chlorophyll)→
Glucose + Oxygen

Four Essential Pillars:

Sunlight
Water
Carbon Dioxide
Chlorophyll

Starch: Glucose synthesized during photosynthesis is stored as insoluble starch for conservation.

Crucial Experiments

Lab Tests

1. The Iodine Starch Test

Boil leaf in water to soften.
Dip in alcohol to decolorize (removes green chlorophyll).
Add diluted Iodine solution.
Result: Green areas turn Blue-Black (starch present). Non-green areas show no change.

2. Is CO2 Needed? (Moll's Half-Leaf)

Place half a destarched leaf inside a bottle with caustic soda (KOH).
Caustic soda absorbs all carbon dioxide in the bottle.
Expose to sunlight, then run Iodine test.
Result: Inner half (no $CO_2$) does not turn blue-black; outer half turns blue-black.

Gas Exchange

Stomata

How do plants breathe and exchange gases like $CO_2$ and $O_2$? They use microscopic pores called Stomata.

Structure & Location

Mainly found on the lower surface of leaves to reduce excessive water loss.

Guard

Guard Cells regulate opening and closing.

Photosynthesis Output:

An experiment using a water plant in a funnel shows Oxygen gas bubbles accumulating in an inverted test tube when exposed to light. This gas intensifies an active flame!

10.3 Vascular Transport

Xylem & Phloem

Plants contain specialized tube-like tissues to transport materials horizontally and vertically:

Feature	Xylem	Phloem
Transports	Water & Minerals	Prepared Food
Direction	Upward (↑) only	Bi-directional (↑ & ↓)
Source	Roots	Leaves (food factory)

Red Ink Experiment: Placing a white flower stem in red ink turns the leaves and petals red, confirming upwards mineral/water transport in Xylem.

10.4 Plant Respiration

Energy Release

Do plants breathe? Yes! Respiration occurs in all living cells (green and non-green) continuously, day and night.

Respiration Equation

Glucose + Oxygen →
Carbon Dioxide + Water + Energy

The energy released is crucial for cellular repair, active transport, and metabolic growth processes.

Germinating Seeds Experiment

Germinating moong seeds kept in a sealed flask produce excess $CO_2$. When routed to a tube filled with lime water, it turns milky, proving carbon dioxide is released during active plant respiration.

Fascinating Facts

Non-Green Leaves: Plants with red, purple, or brown leaves (like Crotons) still photosynthesize! Their rich alternative pigments simply mask the green chlorophyll.
Ancient Botany: The ancient Indian text Vrikshayurveda states: "Trees do not produce fruits and flowers merely because they are planted," documenting detailed organic manure practices used centuries ago.

Know Your Scientist

Rustom Hormusji Dastur (1896-1961)

An eminent Indian plant physiologist and head of Botany at the Royal Institute of Science. He pioneered critical studies on how light intensity, atmospheric temperature, and leaf color variation influence the rate of photosynthesis in local crop varieties.