REPRODUCTION IN ORGANISMS 4

1. Gamete transfer-

• The process of bringing together of male and female gamete for fertilization is called gamete transfer.
• In majority of organisms male gametes are motile and female gametes are non-motile while in algae and fungi both the types of gametes are motile.

• In bryophytes and pteridophytes, gamete is transferred through water.

• In seed producing plants, pollens are transferred to the stigma by pollination.

• In bisexual self-fertilizing plants, anthers and stigma are located close to each other and so transfer of pollen grains is easy. Example- pea.
• In cross-pollinating plants, the agents like wind, insects moving for collecting nectar from the flowers help in pollination.

FERTILIZATION

The process of fusion of male and female gametes to form a zygote is called fertilization or syngamy.

• In rotifers, insects, lizards female gametes develop in to new organisms without fertilization, the process is called as parthenogenesis.

• 2 types of fertilization-

External fertilization-

• In this type of fertilization, syngamy occurs outside the body of organism. Example- in most aquatic organisms like algae, fish, amphibians.

• The major disadvantage of external fertilization is they produce a large number of off springs but the off springs are vulnerable to predators

Internal fertilization-

• Syngamy occurs inside the body of organisms. Example- fungi, birds, mammals.
• Male gametes are released close to the female gametes.

POST- FERTILIZATION EVENTS

Zygote formation

• In some organisms like fungi and algae, the zygote develops a thick wall around it which is resistant to damage and undergoes a period before germination.

• Further development of zygote depends on the type of life cycle of organisms and the environment in which they are surviving.

• In all sexually reproducing organisms, a diploid zygote is formed as a result of fertilization and later the zygote develops into a new organism.

Embryogenesis

• The process of development of embryo from the zygote.
• Embryogenesis includes cell division and cell differentiation in the zygote.
• Cell division increases the number of cells and cell differentiation helps to form tissues and organs to form a fully developed organism

• Depending on the development of zygote inside or outside the body of the female parent, animals are classified into oviparous and viviparous animals.
• Oviparous animals are those which lay eggs and the eggs develop into new organisms. Example- amphibians, fishes, birds, reptiles etc.
• Viviparous animals are those which give birth to their young ones. Example- mammals.

• In some oviparous animals like reptiles and birds the fertilized eggs remain covered by hard calcareous shell and such eggs are called cleidoic eggs.
• In flowering plants, the zygote is formed inside the ovule and the sepals, petals, stamens of the flower usually fall off.
• The zygote develops into embryo
• Ovules develop into seeds
• The ovary develops into the fruit.
• The ovary wall develops into a protective layer called pericarp

SEXUALITY IN ORGANISMS

The flowers having either male or female reproductive structure are called unisexual or dioecious or heterothallic Example- papaya, date palm.

The flowers having both male and female reproductive structures are called bisexual or monoecious or homothallic Example- hibiscus, coconuts

In plants the unisexual male flower is staminate as it bears stamen and unisexual female flower is pistillate as it bears pistil.

Some animals possess both male and female reproductive organs. Such animals are called as bisexual or hermaphrodites or Example- earthworm, frog, bird.

Animals having either male or female reproductive structures are called unisexual or dioecious Example- human.