Biomedicine
Plant Biology + Medicine

Plant Biology & Medicine

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Plant Biology

Plant biology, also known as botany, is the scientific study of plants, including their physiology, structure, genetics, ecology, distribution, classification, and evolution. It explores how plants grow, reproduce, interact with their environment, and contribute to the ecosystem. Understanding plant biology is crucial because plants provide oxygen, food, medicine, and materials, and play a key role in climate regulation and the global carbon cycle

Plant Cell Structure

Plant cells have unique parts that help them grow, store energy, and make food from sunlight. This section breaks down each key structure — like the cell wall, chloroplasts, and vacuole — and explains how they work together to keep plants alive and healthy.

Cell wall & Cell Membrane

The cell wall is a rigid outer layer made mostly of cellulose. It surrounds the plant cell and provides structural support, helping the plant maintain its shape. It also protects the cell against physical damage and prevents excessive water intake by creating pressure resistance.

The cell membrane is a thin, flexible layer located just inside the cell wall. It controls the movement of substances in and out of the cell, allowing nutrients to enter, waste products to leave, and communication signals to pass between cells.

Nucleus

The nucleus is the command center of the cell. It contains the cell’s DNA, which carries instructions for all cellular activities. The nucleus controls growth, reproduction, and the production of proteins by regulating which genes are active.

Central Vacuole

The central vacuole is a large, fluid-filled sac located at the center of most plant cells. It stores water, nutrients, and waste products. It also maintains internal pressure (turgor), which keeps the plant upright and supports cell structure.

Chloroplasts

Chloroplasts are green, oval-shaped organelles responsible for photosynthesis. They contain chlorophyll, which captures sunlight and uses it to convert carbon dioxide and water into glucose (sugar), providing energy for the plant.

Endoplasmic Reticulum

The endoplasmic reticulum is a network of membranes that helps with the production and transport of materials. The rough ER, covered with ribosomes, synthesizes proteins. The smooth ER is involved in making lipids and detoxifying chemicals.

Mitochondria are bean-shaped organelles known as the powerhouses of the cell. They convert the chemical energy stored in glucose into ATP (adenosine triphosphate), which is used to power the cell’s activities.

Mitochondria

Golgi apparatus

The Golgi apparatus is a stack of flattened membranes that modifies, packages, and distributes proteins and other molecules. It prepares materials for delivery to different parts of the cell or for secretion outside the cell.

Photosynthesis

    • Sunlight excites chlorophyll, splitting water (H₂O) into oxygen (O₂), protons (H⁺), and electrons.

    • Produces ATP and NADPH, which store chemical energy

    • Uses ATP and NADPH to synthesize glucose.

    • This process is essential not only for plant growth but also for sustaining life on Earth by producing oxygen and forming the base of food chains.

Plant Classification

Plants are divided into major groups based on evolutionary traits:

Non-vascular plants (Bryophytes): No xylem/phloem; rely on diffusion. Example: mosses.

Seedless vascular plants (Pteridophytes): Xylem/phloem present; reproduce via spores. Example: ferns.

Gymnosperms: Produce naked seeds in cones (no fruit). Example: pine, spruce.

Angiosperms: Most advanced; have flowers and fruits with enclosed seeds. Example: roses, wheat, apple trees.

    • A waxy, waterproof layer covering the upper surface of the leaf.

    • Function: Protects the leaf from water loss and provides a barrier against pathogens.

    • It helps the plant conserve moisture, especially in dry environments.

    • A single layer of flat cells just beneath the cuticle.

    • Function: Protects internal tissues and allows light to pass through to the photosynthetic cells below.

    • These cells do not contain chloroplasts, so they don’t carry out photosynthesis.

  • A layer of tall, tightly packed cells beneath the upper epidermis.

    • Function: This is the main site of photosynthesis. The cells are full of chloroplasts to absorb sunlight efficiently.

    • Palisade cells are arranged like columns to maximize light absorption.

    • Located beneath the palisade layer.

    • Made up of loosely arranged cells with lots of air spaces between them.

    • Function: Allows gas exchange (CO₂ in, O₂ out) through the air spaces, and also contributes to photosynthesis.

    • Found in the veins (vascular bundles) of the leaf.

    • Function: Transports water and minerals from the roots to the leaf.

    • Helps keep the cells hydrated so photosynthesis can occur.

    • Also part of the veins, usually located below the xylem.

    • Function: Transports sugar and other nutrients (produced during photosynthesis) from the leaf to other parts of the plant.

    • A single layer of cells on the underside of the leaf.

    • Function: Protects the internal tissues and contains important pores (stomata) for gas exchange.

    • May also have a thin cuticle to reduce water loss.

    • Small openings or pores in the lower epidermis.

    • Function: Allow gases (CO₂, O₂) to move in and out of the leaf and control water vapor loss.

    • Each stoma is surrounded by guard cells that open and close the pore depending on conditions (like sunlight or water availability).

Plant Tissue

Plant Reproduction

  • Asexual reproduction

    Only one parent.

    Offspring are genetically identical (clones).

    Runners: Horizontal stems (e.g., strawberries).

    Cuttings: New plant from a piece of leaf/stem.

    Bulbs/Tubers: Underground storage organs (e.g., onions, potatoes).

  • Sexual Reproduction

    Involves two parents.

    Occurs via flowers, which contain male (stamen) and female (pistil) organs.

    Produces seeds that grow into genetically unique offspring.

    Sexual reproduction increases genetic diversity, which helps plants adapt to changing environments.

Pollination

Pollination is the process of transferring pollen from the male to the female part of a flower. It can be done by wind, water, insects, or animals. After pollen lands on the stigma, it grows a tube down to the ovule, where fertilization occurs. The fertilized egg develops into a seed, and the surrounding ovary often becomes a fruit. This process ensures the continuation of plant species and is crucial for agriculture and ecosystems.

  • Biotic pollination: Done by animals like bees, butterflies, bats, birds.

  • Abiotic pollination: Wind or water disperses pollen (e.g., in grasses).

    After pollination:

    • Pollen tube forms, allowing sperm cells to reach the ovule.

    • One sperm fertilizes the egg → zygote; another may fuse with two polar nuclei → endosperm (nutritive tissue).
      This double fertilization is unique to angiosperms and ensures food is available for the developing embryo.

Seed Germination

Seed germination is when a seed begins to grow into a new plant. For this to happen, the seed needs water, oxygen, and the right temperature. Once conditions are right, the seed absorbs water, enzymes activate, and the embryo inside starts to grow. The root emerges first to anchor the plant and absorb water, followed by the shoot, which reaches for light. Germination marks the start of a plant’s life cycle

Conditions Needed:

  • Water: Activates enzymes that break down stored food.

  • Oxygen: Needed for cellular respiration (energy production).

  • Proper temperature: Varies by plant type.

Seed Structure:

  • Embryo: Tiny baby plant (root, shoot, and leaves).

  • Cotyledon(s): Food storage to feed the embryo.

  • Seed coat: Protective outer layer.

Plant hormones

Plants may seem passive, but they’re surprisingly clever when it comes to self-defense. From releasing toxic chemicals and mimicking other species to summoning insect bodyguards, this TED-Ed video explores the fascinating strategies plants use to survive and outsmart their enemies.

    • Promote cell elongation in stems and roots.

    • Cause phototropism – bending toward light.

    • Stimulate stem and leaf growth, seed germination, and flowering.

    • Often used in agriculture to increase fruit size.

    • Promote cell division and growth in roots and shoots.

    • Help delay aging (senescence) in leaves.

    • A gas that causes fruit ripening, leaf drop, and flower aging.

    • Used commercially to ripen bananas and tomatoes.

    • Inhibits growth during stress (e.g., drought).

    • Causes seed dormancy and stomatal closure.

Plants & Medicine

Plants are fundamental to life on Earth, not only as oxygen producers and the base of food chains, but also as key contributors to medicine. Their ability to synthesize complex chemical compounds has provided humanity with some of its most effective and essential drugs. This section explores how the biology of plants directly contributes to modern and traditional medicine, bridging plant physiology and medicinal treatments.

Plant Secondary Metabolites: Nature’s Chemical Arsenal

While all plants perform basic life-sustaining functions like photosynthesis, they also produce secondary metabolites—specialized compounds not directly involved in growth or reproduction, but essential for defense, pollinator attraction, or stress tolerance. These include:

  • Alkaloids – Nitrogen-containing compounds with potent biological effects.
    Examples:

    • Morphine from the opium poppy (Papaver somniferum) – pain relief.

    • Vincristine from the rosy periwinkle (Catharanthus roseus) – used in chemotherapy.

  • Terpenoids – The largest class of plant chemicals; often aromatic and bioactive.
    Example:

    • Taxol (paclitaxel) from the Pacific yew tree (Taxus brevifolia) – anti-cancer drug that inhibits mitosis.

  • Phenolics – Antioxidant compounds involved in UV protection and pathogen defense.
    Example:

    • Salicylic acid from willow bark (Salix alba), the natural precursor of aspirin.

These compounds often target specific pathways in animal physiology, making them ideal for therapeutic use.

Extraction and Isolation

Compounds are separated from plant tissues using solvents and tested in vitro.

Structure Elucidation

Chemical structure is determined using spectroscopy and chromatography.

Pharmacological Testing

Compounds are tested for safety, efficacy, dosage, and side effects in pre-clinical and clinical trials.

Synthesis and Optimization

Chemists may create synthetic analogs with improved properties (e.g., better absorption, fewer side effects).

From Plant to Pill: Drug Development Process

While many plant-derived compounds are bioactive, not all are immediately safe or effective for human use. The journey from plant extract to pharmaceutical involves;

Key Takeaways–

The Plant as a Solar-Powered Factory

Think of a plant as a solar-powered factory that runs 24/7:

  • The plant cell is like a factory room, with machines (organelles) doing different jobs.

  • The chloroplasts are the solar panels — they capture sunlight and turn it into energy (glucose) through photosynthesis.

  • The cell wall is the factory wall, giving structure and protecting what's inside.

  • The vacuole is the storage tank, holding water and materials needed for operation.

  • The xylem is the plumbing system, bringing water from the ground to where it's needed.

  • The phloem is the delivery system, shipping food (sugars) from the leaves to other parts of the plant.

  • The stomata are ventilation ducts, opening and closing to let gases in and out.

  • The nucleus acts like the control center, directing all the factory's operations.

Just like a well-run factory, every part of a plant works together — using sunlight, water, and carbon dioxide to create food, grow, and support life around it. An entire system of such plants is the root of the medicinal world and treatment.