Define the following terms: (i) Inflorescence (ii) Fruit (iii) Seed. Briefly describe how the following processes occur: (i) Double Fertilization in an angiosperm (ii) Cross-pollination in a maize plant.

Here are the solutions to your biology questions.

3. Definitions and processes

• a) Define the following terms:

  • (i) Inflorescence: An inflorescence is a cluster or arrangement of flowers on a plant stem, often with a specific pattern or structure, such as a spike, raceme, or panicle.
  • (ii) Fruit: A fruit is the mature, ripened ovary of a flowering plant, typically containing the seeds. Its primary function is to protect the seeds and aid in their dispersal.
  • (iii) Seed: A seed is a mature ovule containing an embryo, along with stored food reserves, enclosed within a protective seed coat. It is the unit of reproduction in seed plants.

• b) Briefly describe how the following processes occur:

  • (i) Double Fertilization in an angiosperm: Double fertilization is a unique process in angiosperms. After a pollen grain lands on the stigma and germinates, a pollen tube grows down the style, carrying two male gametes. The pollen tube enters the ovule and releases these gametes into the embryo sac. One male gamete fuses with the egg cell to form a diploid zygote. The other male gamete fuses with the two polar nuclei in the central cell to form a triploid primary endosperm nucleus. This simultaneous fusion of two male gametes with two different female structures is called double fertilization.
  • (ii) Cross-pollination in a maize plant: Maize (corn) is a monoecious plant, meaning it has separate male and female flowers on the same plant. The male flowers are in the tassel at the top, producing large amounts of light, dry pollen. The female flowers are in the ear, with long, silky stigmas (silks) emerging from the husks. Cross-pollination occurs primarily by wind. Wind carries pollen from the tassel of one maize plant to the silks of another maize plant. The silks are highly effective at catching airborne pollen, leading to fertilization and kernel development.

4. Growth

• a) What is growth? Growth is an irreversible increase in size, mass, and volume of an organism or its parts, resulting from cell division, cell enlargement, and differentiation. It is a fundamental characteristic of living organisms.

• b) Discuss the internal and external factors affecting plant growth.

  • Internal Factors:
    • Hormones (Phytohormones): Plant hormones like auxins, gibberellins, cytokinins, abscisic acid, and ethylene regulate various aspects of growth, including cell division, elongation, differentiation, flowering, fruiting, and dormancy.
    • Genetic factors: The plant's genotype determines its inherent growth potential, maximum size, and developmental patterns.
    • Nutrient reserves: Stored carbohydrates and other nutrients within the plant influence initial growth and development.
  • External Factors:
    • Light: Light intensity, quality (wavelength), and photoperiod (duration of light/dark) affect photosynthesis, phototropism, and flowering.
    • Temperature: Optimal temperatures are crucial for enzyme activity, metabolic rates, and overall growth. Extreme temperatures can inhibit or damage growth.
    • Water: Water is essential for photosynthesis, turgor pressure, nutrient transport, and cell expansion. Water availability directly impacts growth.
    • Nutrients (Minerals): Availability of essential macronutrients (e.g., N, P, K) and micronutrients (e.g., Fe, Zn, Mn) from the soil is vital for synthesizing plant components and metabolic processes.
    • Carbon dioxide: CO$_2$ concentration in the atmosphere is a key substrate for photosynthesis, directly influencing growth rate.
    • Soil pH: Soil pH affects nutrient availability and microbial activity, which in turn impacts plant growth.

• c) Distinguish between primary and secondary growth.

Feature	Primary Growth	Secondary Growth
Location	Apical meristems (root and shoot tips)	Lateral meristems (vascular cambium, cork cambium)
Result	Increase in length of roots and shoots	Increase in girth/thickness of stems and roots
Tissues Involved	Protoderm, ground meristem, procambium	Vascular cambium (produces secondary xylem/phloem), cork cambium (produces periderm)
Occurrence	Occurs in all vascular plants	Occurs mainly in woody dicots and gymnosperms; rare in monocots
Function	Elongation, formation of primary tissues	Widening, formation of wood and bark