Plant and Human Reproduction and Inheritance Study Guide

Plant Sexual Reproduction and Flower Anatomy

• Flowering plants can reproduce either asexually or sexually. Sexual reproduction in plants involves both male and female structures located within the flower.

• The Stamen (Male Reproductive Structure):

  • Anther: The structure containing pollen grains, which produce male gametes (sperm).
  • Filament: The supporting stalk that holds up the anther.
  • Memory Tip: Remember that the staMEN is the MALE reproductive part of the flower.

• The Carpel (Female Reproductive Structure):

  • Stigma: The terminal surface at the end of the carpel that pollen grains attach to.
  • Style: The rod-like structural section that supports the stigma.
  • Ovary: The organ containing female gametes (eggs) stored inside individual ovules.

• Principles of Pollination:
  • Pollination Definition: The process of transferring pollen from an anther to a stigma, enabling male gametes to fertilise female gametes during sexual reproduction.
  • Cross-Pollination: A form of sexual reproduction where pollen is transferred specifically from the anther of one plant to the stigma of a different plant.
  • Pollination Vectors: Cross-pollinating plants rely on external vectors such as insects or wind to complete pollen transfer.

Plant Pollination Adaptations

• Plants possess distinct anatomical adaptations depending on whether they are pollinated by insects or by wind currents.

• Insect-Pollinated Plant Features:

  • Petals: Large, brightly coloured petals to attract pollinating insects.
  • Scent and Nectaries: Scented flowers and nectaries (specialized glands that secrete nectar) to attract insects.
  • Pollen Grains: Production of large, sticky pollen grains that readily adhere to the bodies of insects as they travel between plants.
  • Stigma: A sticky stigma surface to ensure that pollen carried by visiting insects sticks firmly to it.
  • Examples: Roses possess large, brightly coloured petals and strong scents to attract insects.

• Wind-Pollinated Plant Features:

  • Petals: Small, dull petals, as attracting insects is unnecessary.
  • Scent and Nectaries: Complete absence of nectaries and strong scents.
  • Pollen Grains: Production of high quantities of small, light pollen grains that can easily be carried across distances by the wind.
  • Filaments and Anthers: Long, dangling filaments that position the anthers outside the flower structure, maximizing exposure so pollen is easily blown away.
  • Stigma: A large, feathery stigma designed to capture drifting pollen grains as wind carries them past. The stigma typically hangs outside the flower as well.
  • Examples: Feathery grass flowers found in long meadows and fluffy willow catkins.

• Identification and Diagnosis:
  • Flowers with bright petals, scent, and sticky pollen are insect-pollinated.
  • Flowers with feathery exposed stigmas, hanging external anthers, dull petals, and no scent are wind-pollinated.

Fertilisation and Germination in Flowering Plants

• Fertilisation Process:

  1. A pollen grain lands on the stigma of a flower (delivered via insect or wind).
  2. A pollen tube grows directly out of the pollen grain, extending down through the style, into the ovary, and entering an ovule.
  3. A nucleus from the male gamete travels down the pollen tube to fuse with the female gamete nucleus inside the ovule.
  • Definition of Fertilisation: The fusion of male and female gamete nuclei to form a zygote.
  • Embryo Formation: The resulting zygote undergoes cell division via mitosis to form an embryo.
  • Seed and Fruit Development: Each fertilised female gamete develops into a seed. The surrounding ovary grows and turns into a fruit surrounding the seed.
  • Species Compatibility Restriction: Flowering plants can only be fertilised by pollen grains from the exact same species or a closely related species.

• Conditions Required for Seed Germination:

  • Seeds remain dormant until external environmental conditions become optimal for growth.
  • Water: Essential to activate the metabolic enzymes that break down stored food reserves within the seed.
  • Oxygen: Required for cellular respiration, which releases energy from food stores needed for seedling growth.
  • Suitable Temperature: Required to provide the optimal temperature environment for seed enzymes to function effectively (varies based on plant species).
  • Constraint: Germination will commence only when all three suitable conditions are met simultaneously.

• Sequential Stages of Seed Germination:

  1. The seed absorbs water, activating enzymes and using its stored food energy to begin growth.
  2. The primary root (embryo root) emerges and grows downwards into the soil.
  3. The primary shoot (embryo shoot) grows upwards toward the surface.
  4. Secondary roots branch out, and the first green leaves appear above ground.

• Energy Sources During Germination:

  • Seed Anatomy: A fully developed seed consists of an embryo (embryo root and embryo shoot) and a food store wrapped inside a protective hard seed coat.
  • Respiration Phase: As germination begins, the seed breaks down its internal food store into glucose for respiration, providing energy for initial cellular growth.
  • Photosynthesis Phase: Once the shoot develops green leaves above ground, the plant generates its own food energy independently through photosynthesis.

Human Reproductive Systems

• Male Reproductive System Anatomy and Function:

  • Sperm are male gametes produced continuously inside the testes following puberty.
  • Sperm mix with glandular fluids to produce semen, which is ejaculated through the penis into the vagina during sexual intercourse.
  • Testis (plural: Testes): The organ site where sperm cells are manufactured.
  • Scrotal Sac (Scrotum): An external sac hanging behind the penis that holds and protects the testes.
  • Vas Deferens (Sperm Duct): A thick muscular tube carrying sperm from the testis toward the urethra.
  • Glands: Structures that produce the seminal fluid added to sperm cells to create semen.
  • Urethra: The central tube through the penis that conveys semen during ejaculation; urine also passes through the urethra to exit the body.
  • Erectile Tissue: Specialized tissue that fills with blood and swells to cause penile erection.
  • Head of Penis: The sensitive tip of the penis.
  • Foreskin: A protective skin layer covering the head of the penis (which may be surgically removed).

• Female Reproductive System Anatomy and Function:

  • Ova (singular: Ovum) are female gametes (eggs). A single ovum is released approximately every $28\text{ days}$ from one of the two ovaries.
  • The released ovum enters the Fallopian tube, which serves as the location where sperm deposited in the vagina during sexual intercourse may meet and fertilise it.
  • Unfertilised Ovum: If fertilisation does not occur, the ovum breaks down and exits through the vagina.
  • Fertilised Ovum: If fertilised, the ovum begins dividing into multiple cells, travels down the Fallopian tube to the uterus (womb), and implants into the endometrium (uterus lining) to grow into an embryo.
  • Ovary: The organ responsible for producing ova and female sex hormones.
  • Fallopian Tube (Oviduct): A muscular channel carrying ova from the ovary to the uterus.
  • Uterus (Womb): The muscular organ where an embryo implants and grows throughout pregnancy.
  • Muscular Uterus Wall: The strong muscular structural layer of the uterus.
  • Endometrium (Uterus Lining): A blood-rich tissue layer that provides implantation support and nourishment for an embryo.
  • Cervix: The narrow muscular neck at the base of the uterus.
  • Vagina: The canal into which sperm are deposited during intercourse.
  • Vulva: The external anatomical structures of the female genitalia.

Puberty and the Menstrual Cycle

• Hormonal Regulation at Puberty:

  • At puberty, the endocrine system secretes key sex hormones: testosterone in males and oestrogen in females. These hormones drive the development of secondary sexual characteristics.

• Secondary Sexual Changes Caused by Oestrogen in Females:

  • Growth of underarm and pubic hair.
  • Widening of the hips.
  • Development of breasts.
  • Commencement of ovum release (ovulation) and the start of periods (menstruation).

• Secondary Sexual Changes Caused by Testosterone in Males:

  • Growth of facial, chest, and body hair.
  • Increase in muscle mass and physical body development.
  • Enlargement of the penis and testicles.
  • Onset of sperm production.
  • Deepening of vocal pitch.

• The Four Stages of the Menstrual Cycle:

  • The menstrual cycle operates over a standard total timeframe of $28\text{ days}$:
  • Stage 1 ($\text{Day } 1$ to $\text{Day } 4$): Menstruation begins. The spongy lining of the uterus breaks down and passes out of the vagina for approximately $4\text{ days}$.
  • Stage 2 ($\text{Day } 4$ to $\text{Day } 14$): The uterus lining repairs and builds up again into a thick, spongy layer full of blood vessels, preparing to receive a fertilised egg.
  • Stage 3 ($\text{Day } 14$): Ovulation occurs. An egg matures inside an ovary and is released into the Fallopian tube on $\text{Day } 14$.
  • Stage 4 ($\text{Day } 14$ to $\text{Day } 28$): The thick uterine lining is maintained for roughly $14\text{ days}$ until $\text{Day } 28$. If no fertilised egg implants into the uterine wall by $\text{Day } 28$, the spongy lining begins to break down, and the entire cycle restarts at Stage 1.