Know the general life cycle of an angiosperm. The flower is the reproductive organ of the plant. The male part of the flower makes pollen, which fertilizes an egg in the female part of the plant. A fertilized egg is called a zygote and develops into the embryo (baby sporophyte) which is inside of the seed. The ovule develops into a seed. The ovary develops into fruit. If conditions are right in the ground, a seed will germinate – start growing into a plant (grown up sporophyte).
Know the parts of the flower and what they do. The male part of the plant is called the stamen – it is made up of the anther (makes pollen) and filament (holds the anther up). The female part of the plant is called the carpel – it is made up of the stigma (sticky thing on top where pollen enters), style (connects stigma and ovary) and ovary (has ovules inside). Petals and sepals are modified leaves. Petals are pretty and smell nice to attract pollinators. Sepals protect a growing bud. Some plants have both male and female parts. Some have one or the other.
A composite flower looks like one flower, but it is really many flowers together. The center of the daisy has many flowers – so this is an example of a composite flower. The sunflower is another good example.
Pollination can happen many ways. A major way is by animal pollination – animals that eat nectar from plants get pollen on them while eating. They fly to another plant to get more nectar and drop off pollen. Pollen can also be distributed in the wind, etc.
The male gametophyte is within the pollen grain. The female gametophyte is within the ovule. When making pollen, one cell undergoes meiosis to produce 4 cells. Each one of these will be encased in a pollen grain. Each of these cells will form 2 sperm. So there are two sperm inside of angiosperm pollen. When making eggs, a cell undergoes meiosis and one egg is made. The three other cells produced are sacrificed to have one big egg. During double fertilization, one sperm fertilizes the egg and the other joins the polar nuclei to make a triploid cell which will become the endosperm (food for embryo).
When a pollen grain lands on the stigma, a pollen tube forms to allow the sperm from inside the pollen to travel down into the ovary. In angiosperms, double fertilization happens. One sperm fertilizes the egg to become the zygote and the other sperm joins the polar nuclei to become a triploid cell that will develop into the endosperm.
Pollen has a tough outer covering to prevent water loss. Its also cool looking.
Flowers have strategies to prevent self-fertilization because sexual reproduction and resulting genetic variation is good. When the anthers and stigmas are at different levels, it is more difficult for self-fertilization to happen.
Some plants recognize their own pollen and prevent self-fertilization. They only let in pollen from other plants.
Dicot embryos have two cotyledons (seed leaves).
A seed has 3 main parts: seed coat (protects the seed), embryo (baby sporophyte), and endosperm (food for embryo)
When a seed germinates, water moves into the seed which causes it to expand and “wake up.” Amylase (enzyme that breaks down starch into glucose) starts breaking down starch in endosperm into glucose for the embryo to use to grow and develop. The embryo elongates and produces roots and leaves and will break through the soil so that photosynthesis can begin to make more sugar.
More seed germination.
Hormones can work in two ways: non-polar hormones (like steroids) can cross the cell membrane and directly do something in the cell like turn on a gene. Hormones that are polar cannot cross the cell membrane, so they dock with a receptor in the cell membrane. This causes a series of reactions to occur that causes some response – like turning on or off a gene or enzyme.
This is an example of signal transduction – a signal causing something to happen. The light causes a series of reactions that leads to the production of a transcription factor – which turns on a gene in the nucleus that produces a protein to make the plant more green. Green is good when you are trying to do photosynthesis. When light is available, it makes sense to spend energy to make this protein.
You need to know the major functions of the plant hormones – auxin (primary growth), cytokinins (root growth), gibberellins (germination, flowering, fruit development), abscisic acid (inhibits growth), ethylene gas (fruit ripening), brassinosteroids (inhibits root growth)
Phototropism = plant grows toward the light. This happens because cells on the shady side of the plant grow longer than the cells on the sunny side. This causes leaning. Auxin causes the shady cells to lengthen. Darwin and his dad studied this – they discovered that the cells that control this are in the tip of the plant and light has to reach the tip for leaning to happen.
Auxin causes fibers in cell wall to expand – so the cell elongates.
A plant will grow up before it will grow out. If you pop off the apical meristem (top bud) the plant will grow fuller – gardening tip.
The difference between regular and dwarf varieties of plants is the amount of growth hormone. If you take a dwarf plant and add hormone – it will grow tall.
Gibberellins are involved in fruit development. If you want really big fruit – you can add gibberellins, like they did to the grapes on the right.
Flowering is controlled by a hormone. In this example, the plant only flowers in the light. If you take a plant that is in the light and attach it to a plant that is in the dark, the plant in the dark will flower in addition to the flower in the light. This is because the plant in the dark is receiving the flowering hormone from its neighbor.
More signal transduction: The catipillar eats the leaf. This wounds the leaf which causes a series of reactions which result in the releasing of a compound that attracts a parasitic wasp to attack the caterpillar.
Phytochromes are made of two light-sensing proteins that can move.
Phytochromes move closer to each other in response to red light which is a signal to do things that need to happen in the light like germination, flowering, etc.
Plants have biological clocks – which means that they know when it is day and night, when it is summer and winter, etc.
Plants that flower during the day will open when light is present.
Photoperiodicity has to do with the length of time that it is light outside. Plants that flower during short days (like winter) need a long dark period to know when to flower. Plants that flower during long days (like summer) need a short period of darkness to know when to flower. The signal to flower comes from the length of darkness, not the length of light.
Types of Flowers <ul><li>Complete – have all four organs (sepals, petals, stamens, carpels) </li></ul><ul><li>Incomplete – Lack one or more organs </li></ul><ul><li>Bisexual – has carpels and stamens </li></ul><ul><li>Unisexual – has carpels or stamens </li></ul><ul><li>Monoeicous – stamens and carpels located on same plant </li></ul><ul><li>Dioecious – carpels and stamens located on different plants </li></ul>