Biology : Growth : Cell Division » Cytoplasmic Division

cell growth and cytoplasmic division

Previous Topic Growth In Plant And Animal

Last class we discussed about, growth, mitosis, prophase, metaphase, anaphase and telophase, well I believed you understand, but if you don’t you should always know that, you are free to ask, today’s topic is the continuation of our last topic : Growth

Cytoplasmic Division

Cytoplasmic division : after the division of the nucleus into two daughter nuclei, the cytoplasm then divides into two along the equator of the cell.

In an animal cell, the cytoplasmic division starts by constriction forming around the middle of the cell which continues to deepen until the division is complete. During this completion, two daughter cells are formed, each with the same number of chromatids as the number of chromosomes in the parent cell.top↑

Interphase

Interphase : on the completion of one cell division, the Interphase follows. The Interphase was formerly thought to be a resting period for the cell, but it was later known that, Interphase is the period of synthesis of body materials and preparation for the next division.

During Interphase, each chromatids synthesizes its opposite half to make a chromosome. New protoplasm is synthesized, endoplasmic reticulum, mitochondria, chromosomes and other cell organelles which broke down during mitosis are formed and its grows into a suitable size so that it can be divide again.top↑

Remember that, in last class I said we will expressed a diagram, well here it is;

stages of mitosis

As observe in the diagram above,
a] Interphase : cell is not dividing and no chromosomes is visible.

b] Early prophase : centriole pairs separate and move to opposite poles.
2) Aster rays form around centriole pairs.
3) Spindle fibres develop between the centriole pairs to form a spindle.top↑
4) Chromosomes become visible in nucleus, then shorten and thicken. Each chromosomes can be seen to be made up of two chromatids joined at the centromere

c] Late prophase : nuclear membrane disappears and chromosomes lie free in the cytoplasm.

d] Metaphase : chromosomes come to lie around the equator of the cell.

e] Anaphase : The two chromatids in each chromosome separate at the centrome, and are moved towards opposite poles along the spindle fibres.

f] Telophase : chromatids arrive at the poles,
2) Spindle gradually disappears,
3) A nuclear membrane forms around each set of chromatids
4) And chromatids gradually become invisible.

Differences Between Mitosis In Plant Cell And Animal Cell

The stages of mitosis in a plant cell are similar to those in animal cell except that, in a plant cell;
a] There are no centrosomes, and the formation of spidle fibres goes ahead without the movement of centrosomes towards the poles.top↑

b] Cytoplasmic division in plant cells is not by constriction of the cytoplasm but by the laying down of a cell wall between the two daughter nuclei.

Cell Enlargement And Differentiation

Cell division is usually followed by cell enlargement and cell differentiation. For example, the cells formed by the cambium in a plant, some of the cells formed are specialized into xylem and some are specialized into the phloem.

Brief :

Cambium : is a layer of cells between the xylem and the phloem that is responsible for the secondary growth of roots and stems.
Xylem : is a vascular tissue in plants responsible for distribution of water and minerals taken up by the roots.top↑
Phloem : is a vascular tissue in plants responsible for distribution and transfer of sugars and nutrients manufactured in the shoot.

So back to our course,
In human body, all the cells come from one original cell, the zygote, however, as cell division continues, some cells differentiate into nerve cells, while others into muscle cells, bone cells and skin cells, etc.

Experiment To Observe Cell Division

Materials needed (specimen) : A variety of prepared slides of root tips and microscope.top↑

Procedure
a] Observe each of the slides under microscope.
b] Make a high power magnification drawing of as many as the cells, as you require to give you a complete process of cell division or mitosis.

Conclusions

Mitosis and cell division will be observed clearly through the high power magnification microscope.

Growth Curves

Growth curves : is a pattern by which growth occurs in both plants and animals. Perennial plants have more open growth than animals and grow for relatively much longer periods, even after what is called maturation, but yet the pattern of growth is still similar to that in animals.top↑

Brief

Perennial Plants : are plants that grow for a long period of time (might be 2 years or even more), e.g cocoa tree, mango tree.
Annual Plants : are plants that grow for a short period of time, usually within a year (yearly plants) e.g maize plant.
maturation is the process by which a young plant started becoming mature as a result of differentiation of cells to produce an adult plants.

Experiment To Observe Growth Curve Of Height In Plants

Materials needed (specimen) : seedlings of common fast growing annual pots (e.g okro plant, sunflower, balsam), graph paper and a metre rules.top↑

Brief : you should note that specimen, as you maybe asked to mention or list fast growing annual plants (okro plant, sunflower, and balsam).

Procedure
a] Watering the pot of seedlings, and ensure that it obtains adequate air and sunlight.
b] Measure and record the height (in centimetres) of two or more three seedlings at weekly intervals.
c] Plot the average height of the plants over 8 to 10 weeks on a height/time graph. If you continue for a long period of time, you should obtain a graph not too different from the image-graph below.

Conclusions And Observations

A growth curve is a graph which shows the pattern of or part of growth of an organism with time.
From you graph, calculate how much the plants grew each week by subtracting from each week’s average height from the average height of the plants the week before.top↑

Below is how to construct you table of reading
Growth : table of increment in height

And below is the graph of weekly increments in length of stem

graph of increment in length of stem

That is the weekly increment in height, plot the weekly increment against time as shown below.
Note : your graph should be similar to this.top↑

Growth curve of plant stem

Regions Of Fastest Growth

In plants, do you think different parts of root and stem grow at the same pace? Well you are about to find out.

Experiment To Determine The Region Of Fastest Growth In A Root

Materials needed (specimen) : five cowpea seeds, water, gas jar, marking ink, a pen and a blotting paper.
Procedure
a] Place five cowpea seeds between the wall of a gas jar and a layer of blotting paper that lines the inner surface of the gas jar.top↑
b] Put some water into the gas jar to a level well below the cowpea seeds, so that the blotting paper draw the water up to the seeds.
c] In about four or less days, the cowpea seeds germinate. Select three seedlings with straight radicles. Bring out the seedlings and lay them flat on wet blotting paper.
d] Mark the last 2 cm of each radicle with marking ink into 2 mm portions.
e] Replace the seedlings in the gas jar, between the blotting paper and the gas jar wall, and then place the gas jar in the dark for 48 hours (2 days)

Conclusions And Observations

After 48 hours, that is, 2 days, it will be observed that, some spaces have elongated more than others. The region of greater elongated is a few mm behind the apex of the root, this region behind the apex is called cell elongation.

Experiment To Determine The Region Of Fastest Growth In Length Of stems

Materials needed (specimen) : five cowpea seeds, small plastic pot for planting seeds, water, making ink, pen and garden soil.top↑
Procedure
a] Plant the five cowpea seeds in garden soil in a plastic pot and water the soil to keep it moist. Ensure that the pot is placed in a sunlight reach place.
b] When the seedlings grow up to about 4 cm, use marking ink to mark the shoot apex of two cowpea seedlings into 1 mm spaces and leave it for 48 hours (2 days)
c] Observe the marks, are they still equal in length? In which part of the stem are the division longer than in the other parts.top↑

Conclusions And Observations

It should be observed that, the greatest elongation occurred within a few mm behind the shoot apex.

Environmental Factors That Affects The Rate Of Growth

Several environmental factors affect growth. You may have observed that many plants grow faster in the raining season ( 1st factor), when water is readily available in adequate amounts to plant, the plant tends to germinate more faster than in the dry season e.g mango tree ( perennial plant). But in the dry season, the shoots of some plants die, and the plants survive the dry season by means of seed e.g cowpea, maize or as underground parts e.g tubers, I.e yam, cocoyam, potatoes etc.top↑

Growth requires synthesis of new protoplasm and other body materials such as cellulose (in plants). Food is necessary for synthesis of protoplasm and body materials. Energy (2nd factor) obtained during respiration is also necessary for synthesis of body materials. Warmth (3rd factor) is also necessary for reactions that are brought about by enzymes during respiration or synthesis of body materials.top↑

Environmental Factors Necessary For Growth In Plants

1] Adequate sunlight, carbon dioxide and water (for photosynthesis)

2] Oxygen for respiration

3] Mineral salt for synthesis of proteins, enzymes and other essential substances in the body.top↑

4] Warm temperature for enzymes to catalyze reactions at a suitable speed e.g optimum body temperature of human being 37°C.

Environmental Factors Necessary For Growth In Animals

1] Balanced diet, adequate amounts of carbohydrates, lipids (fat and oil), mineral salts, vitamins, protein and water.

2] Suitable temperature, optimum body temperature, 37°C.

3] Oxygen for breathing and for other activities.

Let call it a day here, till next class, our next topic is regulations of growth by hormonestop↑

Next Topic : Regulation Of Growth By Hormones

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