Chapter 7: How do Organisms Reproduce? - Solutions

Organisms benefit from spore reproduction because:

• Spores are covered by thick protective walls that help them survive unfavorable conditions
• Spores can remain dormant for long periods until conditions become favorable
• Spores are lightweight and can be easily dispersed by wind, water, or animals to new locations
• A single organism can produce a large number of spores, increasing the chances of survival
• Spores can germinate and grow into new individuals when they land on suitable surfaces

Complex organisms cannot reproduce through regeneration because:

• They have highly specialized cells, tissues, and organs with specific functions
• Their body organization is complex with cells organized into tissues, organs, and organ systems
• They require specific arrangements and coordination between different body parts
• Regeneration in complex organisms is limited to repairing damaged tissues, not creating complete new individuals
• They have evolved more efficient reproductive methods (sexual reproduction) that allow for genetic variation

Vegetative propagation is practiced because:

• It allows plants to be grown that have lost the capacity to produce seeds (e.g., banana, rose, jasmine)
• Plants grown by vegetative propagation bear flowers and fruits earlier than those grown from seeds
• All plants produced are genetically similar to the parent plant, preserving desirable characteristics
• It is a faster method of propagation compared to growing from seeds
• It helps in growing plants that are difficult to grow from seeds
• It ensures that specific varieties of plants are maintained without genetic variation

DNA copying is essential in reproduction because:

• It transmits genetic information from parents to offspring
• It ensures the continuity of species by preserving the basic body design
• It provides the blueprint for making proteins that determine an organism's characteristics
• It creates variations through errors in copying, which are important for evolution
• It enables the inheritance of traits from one generation to the next

The roles of seminal vesicles and prostate gland are:

• Seminal vesicles: Produce a fluid that provides nutrition to sperm and helps in their motility
• Prostate gland: Secretes a milky fluid that helps in the transport of sperm and provides nourishment
• Both glands contribute to the seminal fluid that makes up semen
• Their secretions provide a medium for sperm to swim in
• They help neutralize the acidic environment of the male urethra and female reproductive tract

Changes seen in girls during puberty include:

• Increase in breast size
• Darkening of the skin of the nipples
• Growth of hair in armpits and genital area
• Onset of menstruation (menarche)
• Widening of hips
• Increase in body fat, especially around hips and thighs
• Growth spurts in height
• Development of reproductive organs

The embryo gets nourishment inside the mother's body through:

• Placenta: A special tissue that develops between the uterine wall and the embryo
• The placenta contains villi on the embryo's side that increase the surface area for absorption
• On the mother's side are blood spaces that surround the villi
• Glucose, oxygen, and other nutrients pass from the mother's blood to the embryo through the placenta
• Waste products from the embryo are transferred to the mother's blood for excretion
• The placenta acts as a barrier but allows selective transfer of substances

No, a copper-T (intrauterine device) will not protect against sexually transmitted diseases (STDs).

• Copper-T is a contraceptive device that prevents pregnancy by:
• Creating a hostile environment for sperm
• Preventing implantation of a fertilized egg
• It does not provide any barrier protection against STDs
• To protect against STDs, barrier methods like condoms should be used
• Condoms create a physical barrier that prevents the exchange of bodily fluids that can transmit infections

(b) Yeast

Explanation: Yeast reproduces asexually through budding, where a small outgrowth (bud) develops on the parent cell and eventually separates to form a new individual.

(c) Vas deferens

Explanation: Vas deferens is part of the male reproductive system that carries sperm from the testes to the urethra.

(d) pollen grains

Explanation: The anther is the part of the stamen that produces and contains pollen grains, which carry the male gametes.

Advantages of sexual reproduction over asexual reproduction:

• Produces genetic variation in offspring, which helps in evolution and adaptation
• Allows for combination of beneficial traits from two parents
• Provides better chances of survival in changing environments
• Helps in elimination of harmful mutations through genetic recombination
• Creates diversity that can help populations resist diseases and parasites

Functions of testes in human beings:

• Production of male gametes (sperms)
• Secretion of the male sex hormone testosterone
• Testosterone brings about changes in boys during puberty
• Regulation of sperm production
• Development of male secondary sexual characteristics

Menstruation occurs because:

• The uterus prepares every month to receive a fertilized egg by thickening its lining
• If fertilization does not occur, the egg disintegrates
• The thickened uterine lining is no longer needed
• The lining slowly breaks down and is shed through the vagina as blood and mucous
• This cycle repeats approximately every month

A labelled diagram of the longitudinal section of a flower would show:

• Sepals: Outermost green leaf-like structures that protect the flower in bud stage
• Petals: Colorful structures that attract pollinators
• Stamens: Male reproductive parts consisting of:
• Anther: Produces pollen grains
• Filament: Stalk that supports the anther
• Pistil: Female reproductive part consisting of:
• Stigma: Sticky top part that receives pollen
• Style: Elongated middle part
• Ovary: Swollen bottom part containing ovules

Different methods of contraception include:

• Barrier methods: Condoms (male and female) that prevent sperm from reaching the egg
• Hormonal methods: Oral pills, injections, or implants that prevent ovulation
• Intrauterine devices (IUDs): Copper-T or hormone-releasing devices placed in the uterus
• Surgical methods: Vasectomy (in males) or tubectomy (in females) to block reproductive tracts
• Natural methods: Avoiding sex during fertile periods
• Chemical methods: Spermicides that kill or disable sperm

Reproduction provides stability to populations of species by:

• Replacing individuals that die, thus maintaining population size
• Ensuring continuity of species over generations
• Maintaining the balance in ecosystems by preserving species interactions
• Allowing adaptation to changing environments through genetic variations
• Preserving the gene pool of the species

Reasons for adopting contraceptive methods include:

• To prevent unwanted pregnancies
• To plan and space childbirth for better maternal and child health
• To protect against sexually transmitted diseases (in case of barrier methods)
• To allow individuals to pursue education and career goals
• To manage family size according to economic capabilities
• To prevent health risks associated with frequent pregnancies
• To contribute to population control for sustainable development