Plant and Animal Reproduction

• Plant and animal reproduction involves comparing and contrasting processes like reproduction, development, nutrition, gas exchange, transport/circulation, regulation of body fluids, chemical and nervous control, immune systems, and sensory and motor mechanisms.

Plant Reproduction

• Plant reproduction is the production of new offspring.
• This can occur sexually or asexually.
• Sexual reproduction involves the fusion of gametes.
• It creates offspring genetically different from their parents.
• Sexual and asexual reproduction in flowering plants is the basis of agriculture.

Sexual Reproduction in Plants

• Sexual reproduction requires genetic material (DNA) from two parents.
• Parent plants have male and female sex cells called gametes.
• Fertilization is the process where genetic material from male and female gametes combines to produce offspring.
• The product of sexual reproduction is seeds.
• Seeds from fertilization contain genetic material from both parents.
• The resulting offspring are not genetically identical to either parent.
• Genetic diversity helps plants survive environmental changes.
• Pollination is the process through which flowering plants reproduce sexually.
• Flowers contain male sex organs called stamens and female sex organs called pistils.
• The anther, part of the stamen, contains pollen.
• Pollen contains the male gametes.
• For reproduction to occur, pollen must move to the stigma, which is part of the pistil.
• Sepals are the outermost, green parts of the flower protecting it before it opens.
• Petals are inside the sepals and are usually colourful, and are modified leaves.
• Stamens contain a filament topped by pollen-producing cells.
• The innermost part of the flower is the carpel.
• The carpel contains the ovary, which houses the eggs or ovules.
• Pollen from another flower is needed for fertilization of an ovule for seed development.
• Self-pollination is when a plant's pollen fertilizes its ovules.
• Cross-pollination occurs when wind or animals move pollen from one plant to another.
• Cross-pollination helps maintain genetic diversity in species.
• Some plants have features preventing self-pollination, such as pollen and ovules developing at different times.
• Pollinators are animals moving pollen between plants.
• Insects (bees, butterflies, moths, beetles) and some birds (hummingbirds) are pollinators.
• Certain mammals also move pollen between plants.
• Flowers attract pollinators with colors and smells.
• Pollen sticks to a pollinator's body as it feeds on nectar.
• Fertilization follows pollination, where male gametes from pollen join female gametes in the egg or ovule.
• Fertilization creates fruit containing seeds.
• Some fruits are fleshy or dry.
• Animals eat fruit and expel waste containing seeds, helping plants expand their habitat.

Asexual Reproduction in Plants

• Asexual reproduction requires DNA from only one parent.
• It creates offspring genetically identical to the parent, called clones.
• Clones lack genetic diversity, making them less able to fight disease and adapt to environmental changes.
• Methods of asexual reproduction include vegetative propagation and fragmentation.
• Vegetative propagation involves offspring growing from a part of the parent plant without seeds or spores.
• Garlic, onions, and tulips reproduce using true bulbs.
• True bulbs are short underground stems also called scaly bulbs, surrounded by modified leaves named a tunic
• Crocuses reproduce using corms, similar to true bulbs but with fewer layers.
• Corms are used up during the growing season and replaced by new ones.
• Potato plants reproduce using tubers.
• Tubers produce new plants from stems or growing points called eyes.
• Ginger plants reproduce using rhizomes.
• Rhizomes are stems growing sideways and branch out to produce new points of growth.
• Strawberry plants reproduce using stolons.
• Stolons are branches growing along the ground, anchoring themselves and developing roots.
• Fragmentation involves new plants growing from small parts of a parent plant that fall to the ground.
• Liverworts and mosses reproduce through fragmentation.
• Horticulturists use asexual reproduction through fragmentation, by cutting and planting a leaf or stem in water or soil (propagating from cuttings).

Animal Reproduction

• Animals, like plants, reproduce in two ways: asexually and sexually.
• Asexual reproduction occurs without the fusion of egg and sperm.
• It creates new individuals whose genes come from one parent.
• Sexual reproduction involves the fusion of haploid gametes to form a diploid zygote.
• The female gamete (ovum) is a relatively large, non-motile cell.
• The male gamete (sperm) is generally a smaller, motile cell.
• Sexual reproduction increases genetic variability among offspring through unique combinations of genes from two parents.
• It may enhance reproductive success when environmental conditions change.
• Asexual reproduction enables isolated animals to produce offspring, and allows for rapid colonization of a habitat.
• Asexual reproduction is most advantageous in stable environments because it perpetuates successful genotypes precisely.

Mechanisms of Asexual Reproduction

• A single parent splits, buds, or fragments to produce offspring with identical hereditary traits.
• Fission is the separation of a parent into two or more individuals of approximately equal size (e.g., sea anemone).
• Budding involves new individuals arising from outgrowths of existing ones (e.g., cnidarians and tunicates).
• Fragmentation involves the body breaking into pieces that develop into complete adults (e.g., flatworms).
• Regeneration is the regrowth of lost body parts, often accompanied by fragmentation (e.g., sea stars).

Mechanisms of Sexual Reproduction

• Sexual reproduction involves two parents.
• Each contributes a specialized gamete (egg or sperm) that fuse to form a zygote.
• Fertilization occurs inside (internal fertilization) or outside the body (external fertilization).

Types of Fertilization

• In internal fertilization, the male generally delivers sperm cells directly into the female's body where moist tissues provide a watery medium for sperm movement; common in terrestrial animals, few fish, and some aquatic animals.
• In external fertilization, mating partners usually release eggs and sperm into the water simultaneously, commonly seen in many fish, amphibians, and other aquatic animals, excluding aquatic mammals, sharks, and special types of fish.

Reproductive Variations

• Some animals show unique and tremendous diversity in their methods of reproduction.
• Even members of the same class may differ markedly in their reproductive process.
• Metagenesis is an alternation of asexual and sexual generations referred to as transformation development; an example is hydrozoan Obelia, where a polyp generation produces medusas by budding, and medusas reproduce sexually to give rise to new polyps.
• Parthenogenesis, also known as virgin development, is a form of reproduction where an unfertilized egg develops into an adult animal; honeybees are an example
• Hermaphroditism means a single organism produces both eggs and sperm (e.g., earthworms).
• Hermaphrodites do not self-fertilize; two animals copulate and inseminate each other.