|Science Focus Topic 3 Notes: Plant Reproduction and Breeding||| Print ||
Selective breeding means that people choose specific plants with particular characteristics and encourage these plants to reproduce.
Plants are also bred for ...
their ability to withstand certain environmental conditions (hardiness)
how much food they produce (yield)
their resistance to disease.
their appearance (sweetheart cherries - Summerland Research Station, B.C.)
Types of Plant reproduction
Plants can reproduce in two very different ways. Sexual reproduction involves the production of seeds and fruits from specialized cells of two plants. Asexual, or vegetative reproduction, occurs when a 'parent' plant grows new plants from its roots, stems, or leaves.
In vegetative reproduction, plants produce new plants identical to themselves. In sexual reprocution - reproduction using seeds - the new plants are slightly different from their parents.
The cone is the part of the tree that has a series of woody scales, and come in various shapes and sizes. Both male and female cones are produced by cone-bearing trees. Female cones contain ovules (eggs) - the small bumps at the end of a scale in a cone. Pollen grains (containing sperm) develop on the smaller male cone. Wind carries the pollen grains to the female cones. Although most of the pollen grains never reach the female cones, those that do get caught in the sticky fluid near the ovule. A pollen tube grows to the ovule and sperm is able to ferilize the egg. The process of pollination is complete. Female cones of pine trees matrure, open, and release their seeds during the fall or winter months. (This whole process takes at least two years) The seeds can then be dispersed by various methods and when they get covered they can eventually sprout and become new pine trees.
Flowers use color, scent, nectar to attact animals, so that the pollination process can begin.
Parts of a Flower
Pollination (good visual description at: http://www.botany.uwc.ac.za/ecotree/flowers/pollination.htm )
Pollination can occur by self-pollination or cross-pollination.
From Seed to Fruit
Once a plant is pollinated, a seed is formed. Seed Parts include the living plant (embryo) and the food suppy (cotyledon). The length of time a seed is able to stay alive varies according to the conditions it experiences. The longest-lasting seed was frozen for over 10,000 years before it sprouted and even flowered (p.125).
A fruit is the growing ovary of the plant that swells and protects the developing seeds of a plant, until they are ripe. Not all fruits can be eaten though - a cotton boll is a fruit. (uses for non-edible fruits)
Dispersal is the transportation of seeds away from the parent plant.
Farmers use machines to disperse seeds. Once they have grown into the crop, they are harvested in two steps. A swather cuts the plants and lays them in rows (the stubble - what is left of the plant after being cut - prevents the plant from touching the soil, so the seeds can ripen). A combine then separates the grain from the rest of the plant. (The grain seeds are collected and the straw is baled, or spread evenly over the field).