One harmful substance that can pass through the placenta is nicotine. It is an alkaloid found in the nightshade family of plants.

Nicotine can cause brain damage or low birth weight if consumed by pregnant women.

The structure in the uterus where the exchange of material between the mother and the developing fetus takes place is the placenta. The placenta supplies the fetus with maternal nutrients, and allows fetal waste to be disposed of via the maternal kidneys.

Testosterone influences the formation of sperm cells

Testosterone is a reproductive hormone.

Testosterone influences the formation of sperm cells which are essential in the process of sexual reproduction be human beings. While the testosterone hormone is not directly responsible for manufacturing sperm cells, it is still a part of the process. A man's testis are primarily responsible for two things: sperm cell production, and testosterone production. When testosterone levels drop in the body, a sequence of triggers tells the testis to produce more testosterone and more sperm.

Correct Answer – Option 4 – The level of testosterone may start to decrease

Gland C in males is responsible for production of testosterone. Hence, if the interaction of the pituitary gland with gland C is blocked, the level of testosterone may start to decrease. Hence, option 4 is correct.

Progesterone is a hormone produced in females. Hence, option 1 is incorrect.

The pituitary gland is not evolved to replace a hormone. Hence, option 2 is incorrect.

Gland A is not equipped with receptors to interact with hormone 3. Hence, option 3 is incorrect.

Correct Answer – Option 4 - D

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination. In humans, it is called an embryo from the moment of implantation until the end of the 8th week, where after it is instead called a fetus. The Embryo grows by mitosis which represents division of the cells for growth.

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei.[1] It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two daughter cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle - the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell.

Correct Answer – Option 2 – asexual reproduction

Asexual reproduction is a method of reproduction where only one parent undergoes reproduction resulting in an offspring genetically identical to the clone. Commercially-important plants are often deliberately propagated by asexual means in order to keep particularly desirable traits such as flower color, flavor, etc. This technique of cutting the stem or branch of a parent and rooting this to grow another plant is known as grafting.

Sexual reproduction, gamete production and gene manipulation are methods of reproducing sexually with the involvement of 2 parents resulting in 1 or more offspring. Hence, options 1,3 and 4 are incorrect.

Correct Answer – Option 1

According to the diagram all genetic material comes from 1 parent. Hence, option 1 is correct.

The cell is divided into 2 equal halves. Hence, option 2 is incorrect.

There is no relation to the size of the parent to the genetic material. Hence, option 3 is incorrect.

There is no information about the relationship of the source of the genetic material and the size of the parent. Hence, option 4 is incorrect.

Correct answer: (4) They result without the union of gametes.

All these organisms reproduce by budding or by binary fission. Budding is an asexual means of reproduction in which outgrowths from the parent form and pinch off to live independently or else remain to eventually form extensive colonies. This is exhibited by the sea anemone (1^st organism in the illustration) and yeast (3^rd organism in the illustration).  Binary fission occurs in amoeba (2^nd organism in the illustration), wherein cells divide by mitosis. The union of gametes only occurs during sexual reproduction.

Incorrect answers:

(1) They vary genetically from the parent.

Any type of asexual reproduction produces genetically identical offspring.

(2) They are produced by the union of gametes.

Union of gametes only occurs during sexual reproduction.

(3) They obtain nourishment from a placenta.

Correct answer: (2) meiosis

Structure X represents an ovum, the female gamete of humans. Gametes divide by meiosis, which is a two-stage type of cell division in sexually reproducing organisms that results in gametes with half the chromosome number of the original cell.

Incorrect answer:

(1) mitosis

Mitosis is another type of cell division in eukaryotic cells conventionally divided into the growth period and another four stages. These stages maintain the chromosome number by equally allocating replicated chromosomes to each of the daughter cells. Only meiosis occurs in sex cells or gametes, except for plants.

(3) recombination

Genetic recombination occurs during prophase I of meiosis, specifically during the chromosomal crossover of homologous chromosomes

(4) cloning

Correct answer: (1) Cell division is most rapid at 37^o C between 6 and 8 hours after it began.

A bacterial growth curve can be divided into four phases-lag, exponential, stationary, and death. During the lag stage, the bacteria are just introduced in the medium, which means the bacteria are still maturing and are not yet capable of division. When they start to divide, the exponential phase starts (steep slope), characterized by cell doubling. During this phase, the bacteria divide at a maximum rate until the nutrients become depleted. When the microbial count remains constant (horizontal line), it has reached the stationary phase. The last phase starts when the microbial count starts to go down again.

In the given bacterial curves, the exponential phase started at 2 hours after the culture was placed in the medium under 37^oC, and stopped dividing after the 10^th hour. Most rapid cell division occurred during the 6^th to 8^th hour, as illustrated by the steep slope of the curve.

Incorrect answers:

(2) Cell division is most rapid at 25^oC between 20 and 24 hours after it began.

At 25^oC, cell division started on the 2^nd hour and entered the stationary phase after the 16^th hour. The fastest cell division occurred during the 12^th hour, shown as the steepest slope of the curve.

(3) Cell division is most rapid at 18^oC between 4 and 8 hours after it began.

At 18^oC, cell division (exponential phase) started at the 2^nd hour and stopped at the 20^th hour. Fastest growth in number took place 14-16 hours after introduction of bacteria to the medium, shown in the curve as the steepest slope.

(4) Cell division occurs at the same rate no matter what the temperature.

This statement is false because the steepest slopes of the three curves are not located at the same part of the y axis (time).