features of different plants group
Answers
Explanation:
Adaptations of plants to survive in their natural environment
Green plants may be divided up into a number of different groups, some of which are more common than others. This may be explained by the different adaptations to get round various problems in their natural environment, such as the supply of factors needed by plants.
Let us consider these factors, which may limit the success of plants in growing in certain places, and put them into ecological perspective.
1) The plants we are concerned with here are all green because they contain the pigment chlorophyll which is able to trap energy from sunlight, and thus enable these plants to make their own food by the process of photosynthesis. If they grow larger, they can trap more light. However, with this energy comes another form of energy, heat, which has the bad effect of dehydrating the plant.
2) At the same time, plants need water, and minerals.
Where can they usually get a fairly steady supply of water and minerals from?
> the soil
Can you explain the contradiction caused by a plant growing in response to problems 1 and 2?
> soil is downwards, but plant must grow upwards for more light, so plants must grow in 2 opposite directions
Plants need an efficient water absorbing and conducting system to carry water from one part of their "body" to another, as well as to hold the plant up and form a sort of skeleton.
3) In order for plants, (and animals, for that matter), to produce offspring which are slightly different from one another, the best way to reproduce is by sexual reproduction. This variation should result in some types which are better suited to their surroundings than others, so that evolution can occur as only the "fitter" types are able to survive. However, this type of reproduction requires special cells called gametes to be produced, then brought together, and allowed to fuse to form a single cell combining the features of both. All these cells are very fragile and need special protection, and careful distribution processes.
4) Plants tend to grow throughout their lifetime, so that some of these problems may become more complicated as they get bigger. If a plant is unable to solve these problems, it is unable to grow very big or to spread to new environments.
Plants that we know well ("higher plants") tend to be the more successful ones at adapting to these everyday challenges.
[ For the time being we are ignoring simpler groups like algae, fungi and bacteria, all of which are sometimes lumped together with the "higher plants" we are all fairly familiar with.]
Reproduction methods
Simple plants are small (not very efficient?) and reproduce by spores, which are often very small and numerous. Usually these plants rely on wet conditions so that sex cells can swim from one plant to another. They may not tolerate drying out.
Plants that are more successful have these adaptations :
1) the use of specialised spores called pollen which contain sex cells in a protected package so that movement of sex cells does not need water, and seeds which contain an embryo plant together with a food store so that it can grow into a new plant,
2) flowers, which may be attractive to insects, and allow the transfer of pollen (pollination) to be more efficiently carried out, and which also develop into the fruit, which helps to spread or disperse the seeds to new areas.
Green plants are sometimes divided into seed plants and non-seed plants, or into flowering plants and non-flowering plants. Linked with these obvious features are other important characteristics such as efficient water transport systems and specialisation to reduce water loss, so biologists feel that these distinctions are of fundamental importance.
Look at the pictures of the specimen plants and fill in the gaps in the table below, explaining simply the features shown by each group. Give an example from each group, and estimate its size.
SPECIAL FEATURES (ADAPTATIONS)
PLANT GROUP
roots & water-conducting tissue? sex cells that swim? spores? seeds? flowers and
> fruits?
Mosses and
liverworts
(Bryophytes)
e.g. >.......
size >.......cm no - only
simple
"rhizoids" yes yes - in
capsules no no
Ferns and
horsetails
(Pteridophytes)
e.g. >.......
size >.......m yes - limited yes > yes - on underside of fronds > no > no
Conifers
(Gymnosperms)
e.g. >.......
size >.......m x10
> yes no > pollen = special spores > yes > no
Flowering plants
(Angiosperms)
e.g. >.......
size >.......cm yes no > pollen = special spores yes yes
Each of the more than 350,000 species of plants differs from every other species in one or more ways. However, plants also have many features in common. Based on these similarities, scientists are able to classify distinct plants into 5 groups known as seed plants, ferns, lycophytes, horsetails, and bryophytes.
Seed plants consist of a wide variety of plants that bear seeds to reproduce. Most botanists divide the seed plants into two main groups of plants, angiosperms and gymnosperms. Angiosperms are flowering plants. They make up more than half of the more than 350,000 kinds of plants. These plants produce seeds that are enclosed in a protective seed case. The word angiosperm comes from two Greek words meaning enclosed and seed. All plants that produce flowers and fruits are angiosperms. They include most of our common plants, such as brightly colored garden plants, many kinds of wild flowers, and most trees, shrubs, and herbs. Most of the plants that produce the fruits, grains, and vegetables that people eat are also angiosperms.
The sizes of angiosperms vary greatly. The smallest flowering plant, the duckweed, is only about 0.5 millimeter long. It floats on the surface of ponds. The largest angiosperms are eucalyptus trees. They grow more than 300 feet. Some botanists divide the angiosperm into two smaller groups. Plants in one group called monocotyledon or monocots, grow from seeds that contain a seed leaf called a cotyledon. Plants in the other group called dicotyledons or dicots, have two cotyledons in their seeds.
Gymnosperms include a variety of trees and shrubs that produce naked or uncovered seeds. Most gymnosperms bear their seeds in cones. The word gymnosperm comes from two Greek words meaning naked and seed. Gymnosperms do not produce flowers. This group is made up of such plants as conifers, cycads, ginkgoes, and gnetophytes.