Question

Given below are certain situations. Analyse each and describe its possible impact:
(i) A population of bacteria living in temperate waters whose temperature increased by global warming.
(ii) The sperm encounters the egg when it reaches the oviduct in human females.
(iii) Self pollination does not occur in a flower that contains only pistil.
(iv) Egg does not get fertilised in a human female.
(v) When the seed is placed under appropriate condition of water and air in the soil?

Hint:

Each biological situation has specific impacts: (i) Temperature affects bacterial growth; (ii) Sperm-egg encounter leads to fertilization; (iii) Pistil-only flowers need cross pollination; (iv) Unfertilized egg causes menstruation; (v) Suitable conditions trigger seed germination.

Answer 1

Part (i): Impact of increased temperature on bacteria in temperate waters
Step 1: Understand the situation.
Bacteria living in temperate waters are adapted to a specific temperature range. Global warming increases the water temperature.
Step 2: Possible impacts on bacteria.

• Increased metabolic rate: Bacterial enzymes work faster at higher temperatures (up to an optimum), leading to faster growth and reproduction.
• Population explosion: Faster reproduction may lead to rapid increase in bacterial population.
• Death if temperature exceeds tolerance: If temperature rises beyond the optimum range, enzymes may denature, leading to bacterial death.
• Species composition change: Heat-sensitive bacteria may die, while heat-tolerant bacteria may thrive, altering the bacterial community.
• Increased decomposition rate: Bacteria decompose organic matter faster, affecting nutrient cycling.
• Potential for pathogenic bacteria: Harmful bacteria may multiply, increasing disease risk.

Step 3: Final answer.
Increased temperature may initially increase bacterial growth and reproduction, but excessive heat can kill them. It may also alter species composition and increase decomposition rate. Part (ii): Impact when sperm encounters egg in oviduct
Step 1: Understand the situation.
In human females, fertilization occurs in the ampulla of the oviduct (fallopian tube) when a sperm meets the egg.
Step 2: Possible impacts.

• Fertilization: The sperm penetrates the egg, leading to fusion of male and female gametes.
• Zygote formation: A diploid zygote is formed, which begins cell division (cleavage).
• Pregnancy initiation: The zygote travels to the uterus for implantation, leading to pregnancy.
• Prevention of additional sperm entry: Cortical reaction prevents polyspermy (entry of multiple sperms).
• Activation of egg: Metabolic changes occur in the egg to begin embryonic development.

Step 3: Final answer.
Fertilization occurs, forming a zygote. The zygote undergoes cleavage and implants in uterus, initiating pregnancy. Part (iii): Impact when self pollination does not occur in a pistil-only flower
Step 1: Understand the situation.
A flower containing only pistil (female reproductive part) is a unisexual female flower. It lacks stamens (male parts), so self pollination cannot occur.
Step 2: Possible impacts.

• Cross pollination required: The flower must receive pollen from another flower (of the same species) through agents like wind, water, insects, or animals.
• Dependency on external agents: If pollinators are absent, pollination may fail.
• Genetic diversity: Cross pollination leads to greater genetic variation in offspring.
• No fruit/seed formation if pollination fails: Without pollination, the ovule will not fertilize, and no seeds or fruits will develop.
• Evolutionary advantage: Prevents inbreeding depression and promotes hybrid vigor.

Step 3: Final answer.
The flower must rely on cross pollination. If pollination occurs, seeds form with genetic diversity; if not, no seed formation occurs. Part (iv): Impact when egg does not get fertilised in human female
Step 1: Understand the situation.
In human females, if the egg released during ovulation is not fertilized by a sperm within 24 hours, it degenerates.
Step 2: Possible impacts.

• Menstruation: The thickened uterine lining (endometrium) breaks down and is shed along with the unfertilized egg, resulting in menstrual bleeding.
• No pregnancy: Fertilization and implantation do not occur, so pregnancy does not begin.
• Hormonal changes: Progesterone and estrogen levels drop, triggering menstruation.
• New cycle begins: The menstrual cycle restarts with the follicular phase.
• Egg degeneration: The unfertilized egg disintegrates and is absorbed or expelled.

Step 3: Final answer.
Menstruation occurs as the uterine lining sheds. No pregnancy results, and a new menstrual cycle begins. Part (v): Impact when seed is placed under appropriate conditions of water and air in soil
Step 1: Understand the situation.
A seed requires specific conditions (water, air, suitable temperature) to germinate. When placed in soil with adequate water and air:
Step 2: Possible impacts.

• Seed germination: The seed absorbs water (imbibition), activating enzymes.
• Metabolic activation: Respiration increases, providing energy for growth.
• Radicle emergence: The radicle (embryonic root) grows downward into the soil.
• Plumule emergence: The plumule (embryonic shoot) grows upward toward light.
• Seedling development: The seed develops into a seedling and eventually a mature plant.
• Photosynthesis begins: Once green leaves appear, the plant becomes autotrophic.

Step 3: Final answer.
The seed germinates, producing a radicle and plumule, and develops into a seedling and eventually a mature plant.