Cell Division: Meiosis and Its Importance

The process of cell division for the production of gametes is called meiosis. In human beings and animals meiosis takes place in the testes and the ovaries. In plants meiosis take place in the anthers and ovaries.

Meiosis  results in gametes which have half the number of chromosomes present in the parent cell. This is necessary so that when two gametes fuse in fertilization , the original number of chromosomes in the parent cell is obtained.

 

 

The original number of chromosomes in a parent cell before meiosis is  known as the diploid  number       ( 2n chromosomes).  The number of chromosomes in a gamete at the end of meiosis is called the haploid number ( ( n chromosomes ).

Each parent cell in meiosis  produces four gametes with different combinations of chromosomes because the chromosomes are reshuffled during meiosis.

 

Importance of Meiosis

1. Production of gametes .

Meiosis enable the production of gametes, fertilization cannot take place without the presence of male and female gametes and new organisms cannot be produced.

2. Reduction in chromosome number.

Each gamete has only half of the number of chromosomes of the parent cell. This is necessary because fertilized ovum contains  chromosomes from both the male and female gamete.

3. Maintainence of chromosome number in somatic cells.

Meiosis enable us to maintain the number of chromosomes in our somatic cells at 46 chromosomes.

4. Production of variation.

Meiosis causes genetic variation in the descendants. New individuals do not resemble their parents closely.

This is brought about in two ways:  

(a) Different  combinations of chromosomes due to reshufflement of parental choromosomes during meiosis process.    

(b) Crossing over which took place when chromosomes are arranged along the equatorial plane. In the process the chromatids exchange genes and so increase genetic variation. Genetic variation in a species enables the species to survive.

 

 

 

 

 

 

 

 

Cell Division : Mitosis and Its Importance

Mitosis is the process by which mature cell divides into two new cells. Each new cells possesses the same number of chromosomes as the parent cell.
All cells except reproductive cells, divide by means of mitosis.
In plants, mitosis is actively carried out at the ends of plant shoots and roots.

 

 

Importance of Mitosis:

1. Mitosis produces new cells for :

(a) growth

(b) replacing aging and damaged cells.

2. Mitosis enables organisms to reproduce themselves:

(a) by asexual reproduction e.g binary fission in amoeba and budding in yeast.

(b)  by vegetative reproduction e.g growing tapioca using its stem, growing lotus using its rhizome and growing bryophllum using its leaf.

 

 

 

 

Coordination Between The Nervous System and The Endocrine System

Similarities:

(a) both respond to stimuli
(b) Coordinate the body’s activities and functions
(c) Have target organs

Differences:

The main difference between these two systems is that the nervous system co-ordinates the body through electrical impulses whereas the endocrine system also co-ordinates bodily functions but is composed of glands that excrete hormones. The nervous system controls muscle movement, senses, heartbeat, breathing, digestion, memory and speech whilst the endocrine system controls levels of glucose in the blood, hydration levels, heat productivity, sexual maturity, sperm and egg production and growth of cells and tissues.

The nervous system:
effect is localized
take shorter time to produce a reaction
duration of a reaction is shorter
do not require hormone

The endocrine system:
effect is widespread
take longer time to produce a reaction
duration of a reaction is longer
involve hormone as an organic messenger

Coordination between the nervous system and the endocrine system is very important.

This coordination :
Enable the body to carry out its activities and functions efficiently and smoothly.
Enables the body to respond to stimuli effectively so as to take action quickly and avoid injury.
Enables the nervous system to detect changes in the body or environment and relate it to the endocrine system for producing the hormones required for join response and action.
Without coordination between the nervous system and the endocrine system , the body cannot function as a whole .

 

The Human Nervous System

The human nervous system may be conveniently subdivided into two divisions: the central nervous system (the brain and spinal cord) and the peripheral nervous system (the nerves extending to and from the central nervous system).

The central nervous system is the control centre of the nervous system. The peripheral nervous system link receptors and effectors with the central nervous system. Nerves from the brain are called cranial nerves, wheres those from the spinal cord are called spinal nerves.

The spinal cord of the central nervous system is a white cord of tissue passing through the bony tunnel made by the vertebrae. The spinal cord extends from the base of the brain to the bottom of the backbone. Three membranes called meninges surround the spinal cord and protect it. The outer tissue of the spinal cord is white (white matter), while the inner tissue is gray (gray matter). A central canal in the spinal cord carries cerebrospinal fluid, which provides for the nutrition and gaseous needs of the cord tissue. The neurons of the spinal cord serve as a coordinating center for the reflex arc and a connecting system between the peripheral nervous system and the brain.

The peripheral nervous system is a collection of nerves that connect the brain and spinal cord to other parts of the body and the external environment. It is subdivided into the sensory somatic system and the autonomic nervous system.

The sensory somatic system carries impulses from the external environment and the senses. It consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves. The sensory somatic system permits humans to be aware of the outside environment and react to it voluntarily.

The autonomic nervous system works on an involuntary basis. It consists of two groups of motor neurons and a set of knotlike groups of cell bodies called ganglia. Motor neurons extend to and from the ganglia to the body organs. One subdivision of the autonomic nervous system is the sympathetic nervous system. Impulses propagated in this system prepare the body for an emergency. They cause the heartbeat to increase, the arteries to constrict, the pupils to dilate, and other changes to take place. The other subdivision is the parasympathetic nervous system. Impulses in this system return the body to normal after an emergency has occurred.

 

The Importance of Scientific Investigation

Scientific investigation method is a systematic way of gaining scientific knowledge. It trains us to think critically and creatively and also trains us to be more observant and more analytical. The idea of using scientific method in conducting any investigation is that we should observe carefully and measure accurately, communicate effectively, make inferences rationally and develop hypothesis logically.

The scientific method involves the following steps:-

a) Observing a phenomenon
b) identifying the problem
c) identifying the variables
d) forming hypothesis
e) planning the investigation
f) carrying out the the investigation
g) observing and collecting data
h) analysing and interpreting data
i) making a conclusion
j) writing a report

 

How Will the World End……!

Nothing is forever, even life is subjected to a certain time frame known as the life cycle. Living organisms come, reproduce and then gone after completing their specific life cycles. So the Earth, our lovely planet and our solar system also not forever, everything will come to the end ……..!. To all of us it is a reality that we have to accept, understand and respect. That it is surely going to happened one day. The only thing is we really do not know when the time is? So the best idea for us is to enjoy our lives, hope for the best and prepare for the worst and thanks God for the opportunities to experience the essence of our living in this great beautiful world!.

 

The Earth Magnetic Field Effects on Us

THE TRUTH FROM NASA ON DEC 21 2012: