The functionality of the cells in the living organisms body is numerous and broad to study of. The living organisms will not be complete without the existence of the cell and so the role cell plays in the cell can not be denied. In my last post, I talked about the functionality of cells in the aspect of growth, sensitivity and many more. Today I will be continuing from where I stopped in my last post.
MOVEMENT
Movement is very important, both within cells, for whole cells (for example, Amoeba, Paramecium and white blood cells) and for whole organisms.
Cyclosis is the movement of the cytoplasm within individual cells. Special protein molecules move the cytoplasm, which can be used to move organelles around the cell. This is important in plant cells. It can move the chloroplasts to the position in the cell where they will get the most light. This will change during the day as the Sun moves across the sky.
Some cells have special structural adaptations for movement. Sometimes they move themselves, sometimes they move other substances. These structures are cilia and flagella, They are hair-like projections from the surface of the cell and they contain proteins, which can contract and relax, so the cilia and flagella move.
Cilia are usually found in animal cells and protoctista. They are small, and a cell usually has many cilia. They are small and a cell usually has many cilia. They have two main functions. In Single- celled organisms such as Paramecium, the beating of the cilia moves the whole organism through the water. In multicellular organisms, cilia are found on membranes lining the surfaces of the body. The beating of the cilia moves substances about, such as the mucus lining the breathing system.
Flagella are larger and a cell usually only has one or a small number. They are found on single- celled organisms and beat to move the organism around,
For example, Euglena. The male reproductive cells of primitive plants and most animals also have flagella, for human sperm. The flagella move the male sex cells towards the female sex cell for fertilisation.
Movement is also important in plants. They do not move their whole body about, but as you have seen, parts of the plant move in response to light and gravity, for example, phototropisms. These movements come about as a result of growth that is controlled by the plant hormones known as auxins. How does this work?
Auxins are not like animal hormones, as they have different modes of action. Animal hormones are made in one gland and affect other specific tissues; they are transported to those tissues in blood. Plant hormones are made in several cells and tissues; they can affect the cells in which they are made or they can move, by active transport, diffusion or by mass flow, to other plant tissues. Each plant growth regulator may affect a number of plant tissues. There are other plant growth regulators, besides auxins, namely cytokinins and gibberellins. Indole-3-acetic acid (LAA) is the most important auxin.
Auxins play a part in stimulating the elongation of shoots and can also stimulate roots to swell and cause expansion in fruit. However, in high concentrations, they inhibit elongation in roots. In very low concentrations, they stimulate elongation in roots.
Auxins stimulate enzymes to break some bonds in the cellulose molecules making up the cell walls. The cell walls become less rigid and allow the cells to swell and elongate. As cells elongate, so the
shoots elongate.
Scientists have discovered that the growth region suggests that removal of the tip will not affect the growth of the shoot. However, when the tip of a shoot is removed, the shoot does not grow. It has been found that the groweh hormone, auxin (lAA), is produced in the tip. IAA diffuses from the tip to the growth region to initiate growth.
The fact that 1AA promotes growth in shoots suggests that it is also involved in the responses of the shoots to light and gravity. In phototropisms, shoots lit from only one side respond by growth- the shaded side grows faster than the illuminated side, so the shoot bends over towards the light. LAA promotes growth, so it seems likely that the shaded side of shoots had more IAA than the illuminated side, so the shoot bends over towards the light. IAA promoted growth, so it seems likely that the shaded side of shoots had more IAA than the illuminated side. Since the growth curvature was influenced by light, it suggests that light is somehow involved inthe distribution of IAA in the shoot. Experiments have shown that IAA diffuses away from light.
When a shoot is illuminated on one side, IAA in that side diffuses towards the dark side of the shoot. This causes a build- up of the hormone in the dark side of the shoot. Since growth is directly proportional to the amount of IAA, the dark side will grow faster than the illuminated side.
REPRODUCTION
Reproduction is the abiliiy of living things to produce new individuals of the same type as themselves, Elephants produce baby elephants, tilapias produce young tilapia, breadfruit produce more breadiruit trees. There are different ways in which organisms can reproduce.
The two main types of reproduction are asexual reproduction and sexual reproduction. In asexual reproduction, the offspring are genetically identical to their parent, there is no joining of special sex cells and only one parent organism is involved.
All of the offspring are identical and they are known as clones. Asexual reproduction is common in single celled organisms, some simple animals and many plants.
Sexual reproduction involves the joining of two sex cells (known as gametes), which are usually from two ditferent individuals. The offspring from sexual reproduction have a genetic mixture from each of their parents. They are difterent from their parents and from each other
FORMS OF ASEXUAL REPRODUCTION
Asexual reproduction is a certain way of reproduction. It gives rise to offspring at relatively low risk to the parent organism. In some groups, such as the bacteria, very large numbers of offspring are produced. The disadvantage is that the offspring are genetically identical to their parent unless a mutation occurs within an individual. This makes it very difficult for the group of identical organisms or clones to cope with
changes in the environment, because if one cannot survive, none of them can survive. There are a variety of ways in which asexual reproduction can take place. Three of them are given below.
(1). FISSION
Fission involves the splitting of an individual. It is a method ot reproduction in many invertebrate organisms. As two new individuals are usually formed, it is also known as binary fission. Bacteria and protoctists such as Amoeba undergo this form of asexual reproduction.
Bacteria are capable of enormous increases in numbers under ideal conditions, when they may divide every 20 minutes. All the body cells undergo binary fission during mitosis for growth and repair in all living things. It is a very successful form of asexual reproduction.
(2). BUDDING
Budding in a reproductive sense does not include the production of buds by flowers.
Reproductive budding is when there is an outgrowth from the parent organism that produces a smaller, but identical, individual. This bud eventually becomes detached from the parent and has an independent existence. Yeast cells reproduce by budding. In single- celled organisms like these, the only recognisable difference between budding and binary fission is that, in budding, the parent cell is larger than the bud. Budding is relatively rare in the animal kingdom, but one example is in Hydra.
(3). VEGETATION PROPAGATION
Vegetative propagation is a more complicated form of the budding that occurs in simple organisms, It takes place in fowering plants. A structure forms that develops into a fully differentiated new plant, identical to the parent. lt eventually becomes independent of the parent plant. The new plant may be propagated from the stem, leaf, bud or root of the parent, depending on the type of plant. Vegetative propagation often involves perennating organs, such as tubers, bulbs and corms. These contain stored food from photosynthesis, and can remain dormant in the soil to survive adverse conditions. They are often not only a means of asexual reproduction, but also a way of surviving from one growing season
to the next. Vegetative propagation is also often used by farmers and gardeners to produce new plants.
FORMS OF SEXUAL PROPAGATION
Few organisms rely solely on asexual reproduction. ln most organisms there is also a system or sexual reproduction, which is used in adverse conditions to produce some genetic variety. In many organisms, flowering plants, arthropods and vertebrates in particular, sexual reproduction is the main method of propagating the species.
Although flowering plants and some arthropods can reproduce asexually as well, the vertebrates have almost all lost the ability to do this.
Conjugation is a simple form of sexual reproduction seen in bacteria, protoctista such as Paramecium and filamentous algae such as Spirogyra. Genetic information is transferred from one organism to another by direct contact.
There are no special sex cells. Conjugation introduces variety, which helps the organisms to survive adverse conditions
FUSION OF MALE AND FEMALE GAMETES
Sexual reproduction in animals and Flowering plants involves the formation of special sex cells or gametes. These have half the number of chromosomes ot the original parent cells, When they fuse together during fertilisation, the chromosome number of the new individual is the same as that of the parents. Gametes are formed during a special form of cell division called meiosis.
This only takes place in the sex organs as gametes are formed. It results in the formation of four daughter cells from one parent cell. Each of the daughter cells has half the chromosome number of the parent cell.
Animals and plants have developed many differentways to making sure that the gametes meet and that sexual reproduction is successful. Some plants have evolved complex combinations of colours, Scents and sugary nectar to attract insects and other animals to pollinate them. Other plants release their pollen carrying the male gametes into the
wind. There are also a vast number of strategies for making sure that the seeds that result are dispersed as widely as possible from the parent plant.
In animals, there are many different ways of making sure that the gametes meet successtully.
Fertilisation may occur outside of the bodly (external fertilisation) or inside the body (internal fertilisation). Once fertilisation has taken place, there are varying levels of parental care of the offspring. Many organisms simply release eggs and sperm into the water and provide no care of the offspring at all. Amphibians, reptiles and birds lay eggs. In general, amphibians provide Iess parental care than reptiles, while birds often work very hard to raise their young. In mammals the young develop within the body of the mother.
Once they are born, the female provides all the nutrition that is required by her offspring in the early stages of independent life in the form of milk from her own body.
REFERENCES
. https://training.seer.cancer.gov/anatomy/cells_tissues_membranes/cells/function.html
. https://www.britannica.com/science/cell-biology
. https://www.sciencedirect.com/topics/neuroscience/cell-movement
. https://en.m.wikipedia.org/wiki/Reproduction
. https://sciencing.com/how-do-living-things-reproduce-13426361.html
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