About 1/3 of earth's land surface is used for agriculture.
28. <u>Answer</u>: All mutations do not affect the organisms due to the following reasons:-
1. The DNA consists of both coding and non coding regions. The coding regions are known as exons and non coding regions are called as introns. The <em>non coding regions </em>do not make up the protein. Thus, if the mutations occur in non coding regions they do not affect the organism.
2. There are some mutations that result in the change of the codon but the new codon formed codes for the same amino as the previous one. This is possible because of the degeneracy of genetic code. For eg, AAA codes for lysine, however if the mutation changes this code to AAU then this also codes for lysine. Such mutations are called as <em>silent</em> mutations.
3. There are some mutations which result in the change in amino acid however the new amino acid formed is similar to the previous one in its properties for e.g leucine and isoleucine. Such mutations are called as <em>neutral</em> mutations and they do not affect the organism
29. <u>Answer</u>: 1. The process of mitosis results in the formation of <em>two diploid cells</em> whereas meiosis results in the formation of <em>4 haploid cells.</em>
2. The process of mitosis takes place to produce copies of the <em>body cells </em>whereas the process of meiosis takes place to produce the <em>gametes</em>.
<u>Explanation</u>:-
- <u>Mitosis</u> is a process in which a cell undergoes a single round of division to produce two identical copies of itself . It occurs in 4 phases Prophase, metaphase, anaphase and telophase. This process occurs in the body cells.
- <u>Meiosis</u> is a process in which a cell undergoes two rounds of cell division to produce 4 copies of haploid cells from a single diploid cell. This process takes place for the formation of gametes.
29. <u>Answer</u>:
<em>Pros</em>
1. Genetic engineering helps us to tackle several diseases. There are many diseases which are caused due to genetic mutations. Genetic engineering helps us to rectify these mutations and hence combat such diseases.
2. Genetic engineering helps us to produce new foods which can withstand adverse conditions such as high/low temperatures, low rainfall, are disease and pest resistant etc. This, genetic engineering helps to significantly improve crop production.
<em>Cons</em>
1. Genetic engineering leads to a decrease in genetic diversity.
2. It can lead to a decrease in the nutritional value of food as genetic engineering often causes an accelerated growth of animals and hence, the nutritional valie of poultry foods is compromised.
Answer: Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. ... Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell.
Explanation:
The
patellar reflex is the most common example or a spinal reflex. When the knee is
tapped, the nerve that will receives this stimulus sends an impulse to the
spinal cord and relay it to the motor nerve. This sources the quadriceps muscle
at the front of the thigh to contract and twitch up the leg. This reflex contains
simply two nerves and one synapse. The leg will start to twitch up on the other
hand the brain is just suitable aware of the tap and comprehends the situation.
<span>Subsequently the tap, the leg is routinely lengthy
once and comes to rest. The nonappearance of this reflex is problematical and recognized
as westphals sign this reflex might be lessened or absent in lower motor
neuron lesions and during sleep. </span>