Answer:
Sperm cells are not normally exposed to blood, but if they are, the immune system may produce __<u>auto-antibodies</u>__ against sperm cells' __<u>auto-antigens</u>_ and render someone sterile.
Explanation:
Auto-antibodies are antibodies that can destroy cells from the same organism. They are mistakenly directed against organs or tissues of the same organisms, causing auto-immune diseases or affections. The autoantibodies action occurs when the organism fails in recognizing its own cells and faces them as strange elements.
Auto-antigen is the molecule produces by the body that fails in being recognized due to a break up in the tolerance mechanisms, triggering an immune response.
In the exposed example, sperm cells do not usually mix with blood. So when they do, blood cells recognize them as strange bodies and act against them. Sterility might be an effect of this auto-immune response.
Answer:
The correct answer will be option C- Convergent evolution.
Explanation:
The body shape of dolphins, sharks and penguins show similarity in structure sue to the same niche they inhabit which is the ocean.
All of them exhibit features which helped them survive in ocean-like streamlined bodies, fins and flippers. The dolphin, shark and penguins are not closely related but inherited similar characters (streamlined bodies, fins and flippers) due to the process of convergent evolution. These analogous features helped their survival in the same conditions.
Thus, option C- Convergent evolution is the correct answer.
At about 12 to 16 years old
Answer:
d. The person's blood vessels in the dermis have undergone
Explanation:
Humans are warm-blooded animals and maintain constant body temperature by using the energy produced during metabolism. To maintain constant body temperature, several thermoregulatory mechanisms operate. Skin is also involved in thermoregulation.
The thermoreceptors present in the skin layers sense the drop in the temperature of surroundings and the blood capillaries present in the dermis are narrowed. Constriction of blood vessels of the dermis occurs to reduce the blood supply to the skin and thereby prevent the heat loss from the body. Vasoconstriction of blood capillaries of the dermis and the resultant reduced blood flow impart pale appearance to the light-skinned person in winters.
Crossword
1. hyphae
3. heterotroph
7. eukaryote
8. flagella
11. protists
9. nucleus
10. bacteria
12. prokaryotic
13. autotroph