Plant Essentials: Structure, Function, & Life Cycles

Plant Parts & Functions

• Roots: Anchorage & Absorption

  Roots provide anchorage for the plant and are responsible for the absorption of water and nutrients from the soil.

• Stems: Support & Transport

  Stems hold the leaves, flowers, and fruits, providing structural support. They also transport fluids (water, nutrients, and sugars) throughout the plant.

• Leaves: Gas Exchange & Vital Processes

  Leaves are the primary sites for gas exchange, which is essential for processes like photosynthesis, transpiration, and respiration.

• Flowers: Reproduction

  Flowers are modified leaves specialized for reproduction. They contain the reproductive organs of the plant.

• Fruits: Seed Protection & Dispersal

  Fruits protect the seeds and facilitate their dissemination (dispersal) to new locations.

Plant Tissues & Sap Transport

The raw sap (water and dissolved minerals) is transported from the roots to the leaves through a specialized tissue called xylem, which is composed of xylem vessels.

From the leaves, the processed sap (sugars produced during photosynthesis) is transported to the rest of the plant through an elaborate tissue called phloem, composed of phloem tubes.

It's important to note that if a plant is deprived of carbon dioxide from the surrounding air, its growth will cease.

Key Plant Processes

Photosynthesis: Producing Organic Substances

Photosynthesis is the vital process by which plants produce organic substances (sugars) using light energy. The leaves contain chlorophyll, a pigment that captures light energy. This energy drives a reaction where water (H₂O) and carbon dioxide (CO₂) are converted into sugars (food) and oxygen (O₂).

The oxygen is released into the environment through tiny pores on the leaves called stomata.

The chemical equation for photosynthesis is:

CO₂ + H₂O + Light Energy → Sugar (Food) + O₂

Respiration: Energy Release

Plant respiration is the process where plants take in oxygen from the air to burn sugars (organic compounds) for energy. During this cellular process, water vapor and carbon dioxide are released into the environment.

Oxygen from the air (or dissolved in water for aquatic plants) enters through the stomata of the leaves.

While plants take in carbon dioxide for photosynthesis and release oxygen during the day, they also respire. During daylight hours, the intake of carbon dioxide for photosynthesis is significantly higher, making it difficult to observe the output of carbon dioxide from respiration. The same applies to oxygen.

The chemical equation for respiration is:

Sugars + O₂ → CO₂ + H₂O + Energy

Transpiration: Water Movement & Loss

Transpiration is the process by which plants release water vapor into the atmosphere, primarily through their stomata. As roots absorb water, it is distributed throughout the plant. However, a significant amount of this water is lost through transpiration.

Plants have developed various mechanisms to prevent excessive water loss, especially in dry conditions.

Plant Reproduction & Development

Pollen Grains: Male Gametes

Pollen grains are microscopic structures that carry the male gametes (reproductive cells) of a plant. They are formed within the anthers, which are part of the stamen (the male reproductive organ of a flower), along with the filament.

Calyx & Corolla: Protective Flower Structures

The calyx (outermost whorl of sepals) and the corolla (whorl of petals) together form a protective wrapping for the inner reproductive parts of a flower.

Fruit Types: Fleshy & Dry

• Fleshy Fruits

  In fleshy fruits (e.g., grapes, tomatoes), food reserves accumulate, making them soft and often edible.

• Dry Fruits

  In dry fruits (e.g., peas, nuts), the walls harden to protect the enclosed seed(s).

Seed Structure

A seed has a protective outer covering called the seed coat. Inside, it contains an embryo (the rudimentary plant) and nutritive tissue (endosperm or cotyledons) to support the embryo's initial growth.

Seed Dispersal (Dissemination)

Dispersal (or dissemination) is the process by which seeds are moved from one location to another, facilitating the spread of the plant species.

Seed Germination

Germination occurs when a seed falls to the ground (or is otherwise in suitable conditions) and the embryo within it begins to develop into a new plant.