31.5 The Origin and Evolutionary Importance of Leaves
One branch assumed the role of the est with a mean content of radiolabeled carbon that is about three main axis, while the other was reduced in size and became flat times that of the smallest.
The spaces between the branches of the rate of metabolism become three times higher as the system becomes flattened.
Euphylls have branched vascular systems because of the sporophyte that reaches maturity.
One hypothesis to explain the difference is that the individual veins apparently originated from the separate branches of the larger sporophytes, which are producing the tough spore coating of an ancestral branched stem at a faster rate.
Evolutionary biologists suspect that it would be an additional demand.
The plants with the greatest importance to humans are the seed plants.
Discuss the development of seeds from fertilized ovules.
There are several advantages that seeds provide.
Eggs are produced while enclosed by protective megaspore walls.
Fossil and living plants have leaves and seeds that suggest that female gametophytes need cal innovations originated.
There are leaves in the plant world.
Their flat structure is unique to seed plants.
The most ancient type of leaves are produced by lycophytes and develop into a small egg- producing gametophyte.
Some experts think that these dolls have smaller dolls inside.
The smallest leaves may have come from sporangia.
By contrast to lycophytes, fern and seed plants have leaves with extensive veins.
Pollination provides more surface area for solar energy absorption than does wind or animal transport.
Fertilization occurs in leaves.
Plants are able to seed plants when a male gametophyte extends a slender pollen tube, which allows them to carry two sperm toward an egg.
The tube can grow larger and produce more offspring.
The stem system was dominated by a branched-stem.
Many euphylls are relatively large because of their branched vascular systems.
Fossil evidence shows that pteridophytes might have evolved from ancestors with branchedstem systems.
The goal of the modeling challenge is to come up with a model that compares the density of leaf veins between plants.
The model in Figure 31.21 shows how fern leaves have evolved from ancestors with branching stems.
Imagine if the leaves of some other plant group evolved from stem systems that were twice as branched.
The stem system ancestral to this other plant group had more branches per unit area when flattened.
If the branch density of ancestors is related to vein density of leaves in descendant plants, draw a pair of models that compare the leaves of ferns and this other plant group, emphasizing the vein density in each type of leaf.
An unusual cell that has more than the diploid num was formed when the other sperm fused with different gametophyte.
This cell continues to divide and generate seeds, and it feeds both embryo development and chromosomes.
This endosperm food tissue is found in angiosperm seeds.
The endosperm will be discussed in more detail in Chapter 40.
If an embryo does not form, seeds allow for access to food supplied by the only person who can provide it, ensuring that the food is not wasted.
Seed plants reproduce using both seeds and spores, but they have not replaced them with seeds.
Plants have a number of reproductive advantages.
Changes in pre-existing structures and processes are involved in the evolutionary principle.
Fossils provide some clues about ovule and seed evolution, and other periods, until conditions become favorable for germination and information can be obtained by comparing reproduction in living seedling growth.
Seed coats are often adapted to other plants.
Many plants, like lycophytes and pteridophytes, release one type of winged seeds that are dispersed by wind.
There are other types of gametophyte.
The plants that produce seeds with coverings that attract animals, are considered to be Homosporous, and their gametophytes live which consume the seeds, digest the covering, and eliminate independently and produce both male and female gametangia the bare seeds at some distance from the originating plants.
One of the advantages of seeds is that they can store a lot of produce, which helps embryo growth, and that they can release two different types of spores, which can grow into males and females, and compete for light, water, and female game.
Pro and minerals are also mentioned.
This is important for seeds that have two kinds of spores.
The plants are shown in shady forests.
The sperm of most seed plants can reach eggs without tion of seed plants, which may have been the reason why they had to swim through water.
In contrast to fertilization, it mandates cross-fertilization and is not limited by lack of water.
The sperm and eggs of plants.
Seed plants can be derived from different gametophytes, which are more likely to be found in arid and dry habitats.
The potential for genetic variation is increased by cross-fertilization.
In order to enhance the survival and reproduction of individu in a land habitat, seeds are considered to be a key adaptation.
The evolution of the gametophytes in some plants and the seed plants suggests that these features were acquired early in the evolution of seeds.
Reduction of the number of megaspores to one per megasporangium was one of the events that happened in the evolution of seeds.
Figure 35.14 shows the amniotic egg produced by many animals.
The gametophytes receive pro tection from environmental damage.
Early steps toward seed evolution are constituted by lacy integument.
Only one megaspore per sporangium can be produced.
Having a single megaspore allowed plants to channel more food into each megaspore.
Increased food gives an advantage to developing sporophytes.
Food materials would be able to flow from mature photosynthetic 1mm sporophytes to their dependent gametophytes and young embryos.