1LIFE CYCLES OF PLANTS

ABBOTTS COLLEGEABBOTTS

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TOPICS

DEFINITIONS Alternation of generations Haploid diploid

LIFE CYCLES OF: Moss A flower

Asexual and sexual reproduction

Asexual SexualProduces genetically identical

organismsProduces organisms that are not

genetically identical

Faster process Slower

Replaced damaged cells and tissues Produces sex cells or gametes

Takes place in favourable conditions Takes place in unfavourable conditions

Cells divide by mitosis Cells divide by meiosis

No sexes involved Male and female organisms required

Asexual reproduction = No sex cells or gametes involved. No sexes male or female organisms required.

Sexual reproduction = Sex cells or gametes involved. Male or female organisms required.

Sexual reproduction involves the two alternating processes of meiosis and fertilization.

In meiosis, the chromosome number is reduced from the diploid to the haploid number.

In fertilization, the nuclei of two gametes fuse, raising the chromosome number from haploid to diploid.

Whatever variation in details there may be from one organism to another, these two activities must occur alternately if sexual reproduction is to continue.

ANIMALS

Meiosis generates the haploid gametes — sperm and eggs — directly. These single cells fuse to form the zygote which will develop into another

diploid animal. .

Alternation of Generations

PLANTS

Meiosis and fertilization divide the life of the organism into two distinct phases or "generations".

The gametophyte generation begins with a spore produced by meiosis. The spore is haploid, and all the cells derived from it (by mitosis) are also haploid. In due course, this multicellular structure produces gametes — by mitosis — and sexual reproduction then produces the diploid sporophyte generation.

The sporophyte generation thus starts with a zygote. Its cells contain the diploid number of chromosomes. Eventually, though, certain cells will undergo meiosis, forming spores and starting a new gametophyte generation

Alternation of Generations

Alternation of Generations

PLANTS

ANIMALS

Alternation of Generations

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ALTERNATION OF GENERATIONS

All terrestrial plants have two phases in their life cycles:

A haploid gametophyte generation that alternates with a diploid sporophyte generation

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ALTERNATION OF GENERATIONS

A haploid spore grows into the haploid gametophyte generation that produces gametes

A diploid zygote grows into a diploid sporophyte generation Certain cells undergo

meiosis and form halpoid spores

Which are the start of the new gametophyte generation

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LIFE CYCLE OF A BRYOPHYTE Eg MOSS

Shows a clear alternation of generations Gametophyte is the more prominent phase The sporophyte is attached to it and dependent on it

DIAGRAM OF THE MOSS LIFE CYCLE

Bryophytes

Eg. MossNo conducting tissue (no xylem and phloem)

No proper roots

Gametophyte generation is more prominent

Sporophyte dependant on gametophyte

2n

n

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LIFE CYCLE OF A FLOWERING PLANT

Are the dominant terrestrial plants Shows a clear alternation of generations Gametophyte is less prominent than the sporophyte There are separate male and female gametophytes Both are microscopic with the female gametophyte

dependent on the sporophyte

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THE END