Pathogens are microorganisms that cause infectious diseases - AQA - GCSE Biology Combined Science - Question 4 - 2019 - Paper 1

Method 1: Insecticides.
Reason: Insecticides kill mosquitoes or reduce their population, which decreases the likelihood of bites that transmit malaria.

Method 2: Mosquito nets.
Reason: Mosquito nets act as a physical barrier to prevent mosquitoes from biting individuals while they sleep, lowering the chances of malaria transmission.

1. Nucleus: A bacterial cell does not have a nucleus, while a eukaryotic cell has a defined nucleus containing its DNA.

2. Size: Bacterial cells are generally smaller than eukaryotic cells, which is related to their simpler structure.

Air holes are present in the cap of the culture bottle to allow air or oxygen to enter, enabling the bacteria to respire. This is essential for the growth of bacteria as they need oxygen for aerobic respiration.

Stage A: The population size increases rapidly due to abundant nutrients and favorable conditions.

Stage B: The growth rate may level off as resources become limited, but the population remains high.

Stage C: The population stabilizes as the rate of births equals the rate of deaths, indicating an equilibrium.

Stage D: The population decreases as cells begin to die from lack of nutrients and the accumulation of waste products.

A multicellular organism cannot absorb all the nutrients it needs by diffusion because of its larger size and increased distance from cells to the environment. Given that diffusion is less efficient over longer distances, the volume of a multicellular organism increases faster than its surface area. Thus, it cannot supply sufficient nutrients to all cells solely through the outer surface.

Calculations:
The volume of cube X (bacterial cell) is $(0.0002 ext{ cm})^3 = 8 imes 10^{-12} ext{ cm}^3$.
The volume of cube Y (multicellular organism) is $(11 ext{ cm})^3 = 1331 ext{ cm}^3$.
The surface area of cube Y is $6 imes (11 ext{ cm})^2 = 726 ext{ cm}^2$.
The surface area to volume ratio for cube X is much greater than that for cube Y, illustrating that diffusion alone is inadequate for nutrient uptake in larger organisms.