13. list and describe the 3 types of nematocysts.
a.
b.
c.
14. what causes a nematocyst to discharge?
15. how often can the mechanism in the nematocyst be discharged?
human uses:
16. how do humans use cnidarians?
status & threats:
17. what is coral bleaching?

Question

Accepted Answer

### Question 13
# Brief Explanations:
- **a. Penetrant (or Stenotele)**: These nematocysts have a long, hollow thread that can penetrate the prey's body. They are used to inject toxins into the prey, helping in immobilizing or killing it. The thread is coiled within the capsule and, upon discharge, extends rapidly to pierce the target.
- **b. Volvent (or Desmoneme)**: These have a shorter, thicker thread that is not hollow. They are used to coil around the prey, such as the appendages of small organisms, to hold them in place. The thread wraps around the target, aiding in capturing the prey.
- **c. Glutinant (or Holotrichous Isorhiza)**: These nematocysts have a sticky thread that is used for attachment, defense, or locomotion. The thread can adhere to surfaces or prey, helping in anchoring the cnidarian or capturing small particles or prey.

# Answer:
a. Penetrant (Stenotele): Long hollow thread, injects toxins to immobilize/kill prey.
b. Volvent (Desmoneme): Short thick thread, coils around prey to hold it.
c. Glutinant (Holotrichous Isorhiza): Sticky thread, used for attachment, defense, or locomotion.

### Question 14
# Brief Explanations:
A nematocyst discharges when it is triggered by a combination of mechanical and chemical stimuli. Mechanical stimuli can be contact with prey or other objects, and chemical stimuli can be substances (like certain chemicals on the prey's surface) that the cnidarian's cnidocyte (the cell containing the nematocyst) detects. This triggers a rapid change in the osmotic pressure within the nematocyst capsule, causing the thread to evert (turn inside out) and discharge.

# Answer:
A nematocyst discharges due to mechanical (e.g., contact with prey) and chemical stimuli, triggering osmotic changes in the capsule that evert the thread.

### Question 15
# Brief Explanations:
The mechanism in a nematocyst can be discharged only once. After discharge, the nematocyst is spent and cannot be reused. The cnidocyte containing the discharged nematocyst will eventually be replaced by a new one as the cnidarian produces new nematocysts.

# Answer:
The nematocyst mechanism can be discharged only once; it is then spent and replaced by a new nematocyst.

### Question 16
# Brief Explanations:
Humans use cnidarians in several ways:
- **Food**: Some cnidarians like jellyfish (in some cultures) and corals (indirectly, as coral reefs support fisheries) are used as food.
- **Aquarium Trade**: Colorful cnidarians like certain corals and anemones are popular in the aquarium trade.
- **Medicinal Research**: Some cnidarian toxins and compounds are studied for potential medicinal uses (e.g., painkillers, anti-cancer drugs).
- **Ecotourism**: Coral reefs (formed by corals, a type of cnidarian) attract tourists for activities like snorkeling and diving, boosting local economies.
- **Biological Research**: Cnidarians are studied to understand evolution, development, and cell biology (e.g., their simple nervous systems, regeneration abilities).

# Answer:
Humans use cnidarians for food (e.g., jellyfish), aquarium trade (e.g., corals/anemones), medicinal research (toxins for drugs), ecotourism (coral reefs), and biological research (evolution/development studies).

### Question 17
# Brief Explanations:
Coral bleaching occurs when corals expel the symbiotic zooxanthellae (photosynthetic algae) living in their tissues. This is often triggered by environmental stressors like increased water temperature, pollution, ocean acidification, or changes in light. Without the zooxanthellae, the coral loses its main source of food (the algae produce food via photosynthesis) and its vibrant color, appearing white or "bleached." If the stress persists, the coral may die.

# Answer:
Coral bleaching is the expulsion of symbiotic zooxanthellae from coral tissues (due to stress like heat/pollution), causing corals to turn white and potentially die.

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