B4 Flashcards
Why study angiosperms?
Why study angiosperms?
They have dominated the planet since the late Cretaceous and early tertiary periods. Their evolution and rise to dominance is closely associated with the evolution of many animals groups. Provide livestock with food, us with raw materials. They are a huge, largely untapped resource of medicines and other biotech products. They are an integral part of the ecology and biodiversity of earth.
What Is the classification of angiosperms?
Phylum - anthophyta
Class - magnoliopsida, liliopsida
What are some special features of angiosperms?
Flowers, ovules enclosed in carpels. Carpels develop fruit. Double fertilisation. Nutritional endosperm in seed. Xylem with vessels, phloem with sieve tube elements. Heterosporous with a very reduced male gametophyte (3 cells) and female gametophyte (7 cells). No antheridia and no archegonia. Diverse life forms.
What are some angiosperm life forms?
Herbaceous forms (non-woody’)
Therophytes (annuals), monocarpic (flower, set seed, die), perennials (life more than 2 years)
Wood plants
Climbers
Shrubs
Trees
Also parasitic forms
How are flowering plants classified into families?
Monocots and dicots.
What is the difference between Monocots and dicots?
Monocots - one cotyledon in seed, root xylem and phloem in a ring, vascular bundles scattered in stem, leaf veins form a parallel pattern, flowering parts in threes and multiples of threes
Dicots - two cotyledons in seed, root phloem between arms of xylem, vascular bundles in a distinct ring, lead veins form a net pattern, flower parts in fours or fives and then multiples
What is an example of monocots and dicots?
Monocot - palm tree
Dicot - most trees
What is the life cycle of an angiosperm?
Seed germinates -> seedling (young sporophyte) -> mature sporophyte -> flowers.
Flowers produce stamens (male) and/or carpels (female). Stamens produce pollen, carpels produce ovules. After pollination and fertilisation, seeds are produced in a fruit. Seeds are dispersed but may remain dormant.
What is the flower structure?
Borne singly or grouped together in an inflorescence. Each flower is formed on a receptacle. Sepals form the calyx and petals form the corolla. Stamens form the androecium (male) and carpels form the gynoecium (female).
What are stamens?
They represent microsporophylls in the angiosperm flower. Stamens are made up of a filament and two-lobed anther. Each lobe has a pair of microsporangia. Diploid microspore mother cells in the pollen sacs undergo meiosis to produce tetras of haploid microspores.
How is pollen formed?
Each haploid microspore develops into a pollen grain (male gametophyte = micro gametophyte) At maturity, the pollen grain consists of 3 cells - a tube cell and 2 sperm cells. Pollen grain has inner wall (intine) and a very resistant outer wall (exine) which is often elaborately sculptured. The exine is made of sporopollenin. Mature pollen grains are often packed with nutritious starch or oils. Pollen grains are released from the pollen sacs when the anthers split open.
What are the carpels and what are they made of and how do they form?
Represent megasporophylls, made up of an ovary, style, stigma. Often the ovary is compound e.g. made up of two or more fused compounds. Ovules are attached to the placenta in the ovary. The fertilised ovules become the seeds. Seeds are eventually enclosed within the fruit which has developed from the ovary.
What is the embryo sac?
The diploid ovule has a stalk called the funiculus and nucleus enclosed by 1 or 2 integuments. As single diploid megastore mother cell in the nucleus undergoes meiosis to produce 4 haploid megaspore cells but only one survives. The surviving haploid megaspore enlarges and its nucleus divides mitotically to produce 8 haploid nuclei.
How does pollination and fertilisation occur?
If compatible pollen reaches the stigma surface, it takes up water and germinates -> pollen tube. The pollen tube grows through the stigma and style to the ovule, usually entering via the micropyle. The 2 sperm cells are liberated into the embryo sac, one fuses with the egg cell to form a diploid zygotes the other unites with the 2 polar nuclei to form a triploid cell. This is called double fertilisation. Diploid zygote develops into the embryo. Triploid cell divides to form the endosperm of the seed.
Life cycle of an angiosperm?
Mature flower on sporophyte plant, anther, microsporangium and microsporocytes, microspore, generative cell and tube cell, pollen grains, stigma, pollen, sperm, style, discharged sperm nuclei.
Other part
Ovary, megasporangium, surviving megaspore, pollen tube, female gametophyte (antipodal cells, central cells, synergies, egg, sperm.
Join in the egg nucleus, fertilisation occurs, zygote, nucleus of developing endosperm, germinating seed, mature flower on sporophyte plant.
How does seed and fruit develop?
The ovule becomes the seed and the ovary (carpel) wall and related structures develop into the fruit. The zygote in the ovule becomes the embryo which is nourished by the endosperm. The integument becomes the seed coat.
What is pollination?
Transfer of pollen from stamen to stigma
What is self pollination and why does it occur?
Plants exhibit this is they have low pollen : ovule ratio. Stamens and styles either develop together or are mature for some time. Stamens and styles often near each other in flower. Flowers must be self compatible. Advantages - pollination is assured, disadvantages - inbreeding leads to lower heterozygosity and inbreeding depression. Occasionally outbreeding will increase heterozygosity, some flowers are cleistogamouos (never open), so only self pollination is possible.
Self pollinated plants example?
Many weedy, annuals. Self pollination assures a rapid and high degree of success in seed production.
What is cross pollination and why does it occur?
Essential if outbreeding is to occur, flowers may be self incompatible. Flower design may prevent self pollination. Flowers may show specific adaptations that promote transfer of pollen from one flower to another.
What physical characteristics of flowers prevent self pollination?
Protandry, protogyny, heterostyly, dioecy
What is protandry?
When stamens develop and mature before carpels have receptive style and stigma.
What is protogyny?
When carpels develop and mature before stamens
