Which of the following represents the first line of defense to an intruding pathogen?

Immunologic memory is the hallmark of adaptive immunity.

Immunologic memory enables the host to mount a more rapid and efficient immune response upon subsequent exposure to the antigen.

Choice A is incorrect because rapid recruitment of immune cells to sites of infection and inflammation is a characteristic of innate immunity.

Choice B is incorrect because antigen-independent defense mechanisms are characteristic of innate immunity.

Choice D is incorrect because non-specific host-defense mechanisms are characteristic of innate immunity.

Granzymes.

Granzymes are a family of serine proteases that are stored in and secreted from the cytotoxic granules of cytotoxic T lymphocytes (CTL) and natural killer (NK) cells.

They work in synergy with perforin, a pore-forming toxin, to induce apoptosis in target cells.

Perforin is necessary for the delivery of granzyme B to the target cell cytosol where caspase-dependent and -independent pathways to apoptosis are activated.

Perforins (choice A) are pore-forming toxins that work in synergy with granzymes to induce apoptosis in target cells.

Cytokines (choice B) are signaling molecules that regulate immune responses but do not directly induce apoptosis in target cells.

Interferons (choice D) are a type of cytokine that play a role in immune responses but do not directly induce apoptosis in target cells.

The correct answer is choice A. Thymus.

The thymus is a primary lymphoid organ located in the mediastinum.

It plays a key role in the maturation and differentiation of T-lymphocytes.

Choice B.

Parathyroid is incorrect because the parathyroid glands are small endocrine glands located in the neck that produce parathyroid hormone, which regulates calcium levels in the blood.

Choice C.

Adrenal is incorrect because the adrenal glands are endocrine glands located above the kidneys that produce hormones such as cortisol and adrenaline.

Choice D.

Pituitary is incorrect because the pituitary gland is an endocrine gland located at the base of the brain that produces hormones that regulate growth, metabolism, and reproductive functions.

The correct answer is choice A. Golgi apparatus.

The Golgi apparatus is a membrane-bound organelle that is responsible for transporting, modifying, and packaging proteins and lipids into vesicles for delivery to targeted destinations.

Choice B is incorrect because mitochondria are responsible for energy production.

Choice C is incorrect because ribosomes are responsible for protein production.

Choice D is incorrect because the endoplasmic reticulum is responsible for lipid production and protein production, but not for modifying, sorting and packaging proteins and lipids.

The plasma membrane is the organelle that encapsulates the contents of the cell and plays a vital role in regulating the movement of substances in and out of the cell.

It is a selectively permeable barrier that separates the internal environment of the cell from the external environment.

Choice A is incorrect because ribosomes are organelles involved in protein synthesis, not in regulating the movement of substances in and out of the cell.

Choice B is incorrect because the nucleus is an organelle that contains the cell’s genetic material, not in regulating the movement of substances in and out of the cell.

Choice C is incorrect because mitochondria are organelles involved in energy production, not in regulating the movement of substances in and out of the cell.

The correct answer is choice C. Estrogen.

Estrogen is a steroid hormone responsible for the development of female secondary sexual characteristics such as breast development, menstrual cycle, and widening of hips.

Choice A, Progesterone, is not the correct answer because it is required to maintain pregnancy and delivery.

Choice B, Testosterone, is not the correct answer because it is a hormone produced by the testes which controls the development of male secondary sexual characteristics.

Choice D, FSH (Follicle Stimulating Hormone), is not the correct answer because it stimulates the growth of ovarian follicles in females and regulates spermatogenesis in males.

Viruses use the host’s replication processes to produce progeny virus particles.

Viruses are obligate intracellular parasites, meaning that they require a host cell to replicate.

They hijack the host cell’s machinery to produce new virus particles.

Choice B is incorrect because viruses do not divide inside the host cell.

Instead, they use the host cell’s machinery to produce new virus particles.

Choice C is incorrect because viruses do not have their own replication processes and rely on the host cell for replication.

Choice D is incorrect because while some viruses may destroy the host cell during replication, this is not always the case and is not the primary relationship between viruses and their host cells during replication.

Atomic mass is very close to mass number but with some deviation in the decimal places.

Atomic mass is also known as atomic weight and is the weighted average mass of an atom of an element based on the relative natural abundance of that element’s isotopes.

The mass number, on the other hand, is a count of the total number of protons and neutrons in an atom’s nucleus.

Choice A is incorrect because atomic mass and mass number do not mean the same thing.

Choice B is incorrect because atomic mass is not always greater than mass number.

Choice C is incorrect because atomic mass and mass number are related.

Fertilization.

Fertilization is the process by which male and female gametes fuse to form a zygote.

Oogenesis (choice A) is the process by which female gametes, or eggs, are produced.

Meiosis (choice C) is a type of cell division that results in the formation of gametes.

Mitosis (choice D) is a type of cell division that results in the formation of two identical daughter cells.

In a well-designed experiment, all variables apart from the treatment should be kept constant between the control group and treatment group.

This means researchers can correctly measure the entire effect of the treatment without interference from confounding variables.

Choice B) Independent variable and dependent variable is incorrect because these are not groups but rather variables.

The independent variable is manipulated by the experimenters while the dependent variable is measured to see if it changes as a result of the manipulation.

Choice C) Experimental group and non-experimental group is incorrect because a non-experimental group is not a term used in experimental design.

The correct term for the group that does not receive the treatment is control group.

Choice D) High level and low level of the independent variable is incorrect because these are levels of the independent variable, not groups.

In an experiment, there can be multiple levels of the independent variable, but they are applied to different groups (e.g.

control group, treatment group).