Plant Evolution and Adaptations

Plant Evolution

• Plant evolution includes Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms, evolving from a common ancestor.
• Angiosperms are the most evolved plants with flowers and fruits
• Gymnosperms have pollen and seeds
• Pteridophytes have a vascular system

Characteristics to Classify Plants

• Presence/absence of water-conducting tissues like xylem and phloem is a classifying characteristic
• Dependence on water for reproduction is another
• True roots, stems, and leaves
• Type of reproduction and reproductive structures

Adaptations of Vascular Plants to Cope with Dry Conditions

• Cuticle (waxy covering) and stomata help in preventing desiccation
• Roots assist in nourishment via water and mineral absorption, as well as anchoring
• Vascular tissue (xylem and phloem) carries fluids
• Supporting tissues such as Xylem hold up leaves for photosynthesis
• Reproduction aided by spores and seeds

Alternation of Generations

• This involves rotating through two generations via three processes
• Gametophyte generation makes gametes (sex cells)
• Sporophyte generation makes spores (minute, typically one-celled reproductive unit capable of giving rise to a new individual without sexual fusion)

Gametophyte

• Cell division (mitosis) creates identical cells for growth and repair
• Is haploid (n) containing half the total chromosomes of a cell
• In humans the haploid chromosome number is 23

Meiosis

• Cell division process where the chromosome number is halved to form haploid gametes which forms a new individual through fertilisation

Fertilisation

• Fusing the male and female gamete to form a diploid organism

Sporophyte

• Is diploid (2n) containing the total chromosomes of a cell
• In humans the diploid chromosome number is 46 (23 pairs)

Bryophytes

• Bryophytes need water for reproduction as the male gamete needs to swim to female gamete in water

Bryophytes Life Cycle

• Bryophyte plants make shade for each other thereby preventing water loss
• Bryophytes includes mosses
• Its gametophyte generation is dominant
• Are considered pioneer species; being the first to grow in a new area
• Binds the ground and prevents erosion, enriching ground for other plants

Bryophytes: Poor Adaptation to Life on Land

• No cuticle: Can dry out easily
• No vascular tissue: Limits plant size as water is not transported effectively from rhizoid

Bryophytes: Ecological Importance

• Plays a role in plant succession

Pteridophytes

• True plant containing Xylem and Pholem allowing plants to support more growth
• True roots anchor the plant, and helps it abosrb water and nutrients
• True leaves perform photosynthesis
• Contains Cuticle

Pteridophytes Life Cycles

• Better adapted to life on land but not completely
• The sporophyte is the dominant phase
• Underneath the pinnae, sori can be found which contain sporangia
• Young fern leaves are rolled up to protect the growth point and prevent water loss

Pteridophytes: Ecological Importance

• Plays a role in plant succession creating of a new environment
• Used by florists in bouquets
• Used in medicine such as M.Punctatum for coughs
• Wood from tropical ferns for building material.

Gymnosperms

• Adapted for life on land possessing vascular tissue like xylem and pholem, and true leaves and roots
• Seeds are sexually produced, ensuring genetic variation
• They do not depend on water for fertilization of gametes
• Seed remains dormant to withstand weather conditions.
• Seeds are not enclosed by a fruit
• Endosperm feeds the embryo until it can photosynthesise

Gymnosperms: Pine Trees

• Male cones produce pollen and female cones produce ovules
• Wind pollination is needed (no more water)
• They grow in Cold, windy, dry and sandy habitats

Gymnosperms Importance

• The biggest source of wood for construction (furniture and paper)
• Used to make floors, antiques, and medicine for chest problems

Seed-bearing Plants

• Their gametophytes in size, and no longer depending on water
• Spores of seed plants are either male or female

Seed Bearing V Ferns

• Plant body differentiated into a root, stem and leaf
• Presence of vascular tissue
• They have a dominant and independent sporophyte generation

Evolutionary Advancements of Seed Plants

• Plant body has secondary growth with stems that branch laterally, allowing taller growth
• Pollen via microspores (male gametes) develop pollen tubes with non-motile male gametes carried towards female gamete in ovule
• After fertilization, resistant seeds form which may be dormant including embryonic plant, food storage tissue & a hard protective covering

Adaptations for a Successful Land Life

• Clear progression from Bryophytes to Angiosperms to becoming more adapted to life on land
• Main obstacle to life on land is preventing water loss and ensuring effective gaseous exchange

Pollination

• Transfer of pollen from an anther to the stigma of same/different flower

Wind Pollination

• Lacks scent/nectar, with small/green/brown flowers as pollinators aren't needed
• Male flowers have long filaments with anthers to release quantities of pollen
• Small/light pollen is easily carried by wind

Insect Pollination

• This pollination has large/brightly colored petals and sweet scents to attract
• Nectar feeds insects with sticky/spiky pollen grains that attach to their bodies
• The quantity of pollen is large since visiting insects will eat some

Birds Pollination

• Flowers are brightly coloured to attract birds, and have little/no scent
• Stamens/stigmas protrude beyond petals.
• Large quantities of dilute nectar are produced
• Flowers are bigger than most with birds carried above to reach them

Asexual Reproduction

• A large number of offspring are rapidly produced however there is no genetic variation as all are genetically identical
• If offspring have a weakness or difficulty
• Not reliable to pollinate as does not need pollinators

Sexual Reproduction

• Requires both male and female reproduction and the offspring have the same genetic composition as the parent
• Offspring are genetically different, can withstand conditions, reshuffles genetic code, etc
• Relies on favorable conditions to occur and there may be reduced amount of offspring decreasing chances of survival

Angiosperms

• Vascular tissue i.e. xylem and phloem
• True leaves and roots
• Produces flowers with seeds enclosed
• Seeds or fruits