Question

1. using paramecium as an example, explain how a protist eats, respires, digests food, reproduces, and maintains an internal water balance (osmoregulation), all within its single - celled body.

1. according to current theory, which group of protists is most closely related to animals, and may have given rise to early sponges? what similarities does this group of protists share with modern sponges?

Explanation:

Question 6

• Eating (Feeding): Paramecium uses cilia to sweep food (like bacteria, yeast, or other small particles) into the oral groove, which leads to the gullet. The gullet then forms food vacuoles that enclose the food.
• Respiration: Gas exchange occurs directly through the cell membrane (plasma membrane). Oxygen from the surrounding water diffuses into the cell, and carbon dioxide diffuses out.
• Digestion: Food vacuoles containing food move through the cytoplasm. Lysosomes fuse with the food vacuoles, releasing digestive enzymes that break down the food into nutrients. The nutrients are then absorbed into the cytoplasm, and the undigested waste is expelled through the anal pore.
• Reproduction: Paramecium can reproduce asexually by binary fission, where the cell divides into two identical daughter cells. It can also reproduce sexually through conjugation, where two Paramecia exchange genetic material through a temporary cytoplasmic bridge.
• Osmoregulation (Water Balance): Paramecium lives in a hypotonic environment (water outside has lower solute concentration than inside the cell). Water constantly enters the cell via osmosis. Contractile vacuoles collect the excess water and expel it out of the cell to prevent bursting. The contractile vacuoles work with radial canals that collect water from the cytoplasm and transport it to the contractile vacuoles for expulsion.

• Closely Related Protist Group to Animals: Choanoflagellates are the protist group most closely related to animals and are thought to be the ancestors of early sponges.
• Similarities with Modern Sponges:
• Cellular Structure: Choanoflagellates have a single flagellum surrounded by a collar of microvilli (choanocyte - like structure), similar to the choanocytes (collar cells) of sponges. Choanocytes in sponges also have a flagellum and a collar that helps in filtering food particles from water.
• Feeding Mechanism: Both use their collar - flagellum structure to generate water currents and trap food particles (like bacteria) from the water.
• Colonial Behavior: Some choanoflagellates form colonies, similar to how sponge cells can be organized in a colonial manner (though sponges are considered multicellular, their cellular organization has colonial - like aspects in terms of cell - cell interactions and cooperation).

Answer:

• Eating: Cilia sweep food into oral groove → gullet forms food vacuoles.
• Respiration: Gas exchange (O₂ in, CO₂ out) via cell membrane.
• Digestion: Lysosomes fuse with food vacuoles, enzymes break down food; nutrients absorbed, waste expelled via anal pore.
• Reproduction: Asexual (binary fission: cell divides into two); Sexual (conjugation: genetic material exchange).
• Osmoregulation: Contractile vacuoles collect excess water (from hypotonic environment) and expel it to prevent bursting.

Question 7