Question

using your food web and/or trophic pyramid, answer #22-25.

1. if the grass has 25,000 kcal of energy, how much energy would be available for the rat and arrester?
2. explain what happens to population size as the trophic level increases. why?
3. what is the ultimate source of energy for the ecosystem?
4. what process is powered by the answer to #24? what type of organism performs this process?

Explanation:

Question 22

Step1: Recall energy transfer rule

In a trophic pyramid, energy is transferred with about 10% efficiency between levels (10% rule: only ~10% of energy from one trophic level is available to the next). Grass is a producer (trophic level 1). Let's assume the food web has grass → herbivore (trophic level 2) → carnivore (trophic level 3, like a rat or a snake? Wait, the question says "rat and snake"—so grass (level 1) → rat (level 2, herbivore or omnivore? If grass is eaten by rat, then rat is level 2, snake eats rat (level 3). Wait, the question is "how much energy would be available for the rat and snake?" Let's clarify:

First, grass (producer) has 25,000 kcal.

For the rat (assuming rat eats grass, so rat is primary consumer, trophic level 2):

Step2: Calculate energy for rat

Using 10% rule: Energy available to rat = 10% of grass energy = \( 0.10 \times 25,000 \) kcal = 2,500 kcal.

Then, snake eats rat (secondary consumer, trophic level 3):

Step3: Calculate energy for snake

Energy available to snake = 10% of rat's energy = \( 0.10 \times 2,500 \) kcal = 250 kcal.

Wait, but maybe the food web is grass → rat (level 2), and snake → rat (level 3, snake eats rat). So total for rat: 2,500 kcal; for snake: 250 kcal. Or if the question is total for both? Wait, the wording: "how much energy would be available for the rat and snake?" So sum? 2,500 + 250 = 2,750? No, wait, rat is level 2, snake is level 3. So rat gets 10% of grass, snake gets 10% of rat.

Wait, let's re-express:

• Grass (trophic level 1): 25,000 kcal.
• Energy available to primary consumers (rat, if rat eats grass): \( 25,000 \times 0.1 = 2,500 \) kcal (for rat).
• Energy available to secondary consumers (snake, if snake eats rat): \( 2,500 \times 0.1 = 250 \) kcal (for snake).

So if the question is how much for rat (2,500 kcal) and snake (250 kcal), or total? The question says "for the rat and snake"—maybe total? 2,500 + 250 = 2,750? But usually, each trophic level is calculated separately. Wait, maybe the food web is grass → rat (level 2), and snake is a tertiary consumer? No, probably grass (1) → rat (2) → snake (3). So rat (level 2) gets 10% of grass: 2,500 kcal. Snake (level 3) gets 10% of rat: 250 kcal. So total available for rat and snake: 2,500 + 250 = 2,750 kcal? Or maybe the question is asking for each? Let's check the 10% rule again. The 10% rule states that only about 10% of the energy from one trophic level is passed to the next due to energy loss (respiration, heat, waste, etc.). So:

For rat (primary consumer, eating grass):
Energy = \( 25,000 \times \frac{10}{100} = 2,500 \) kcal.

For snake (secondary consumer, eating rat):
Energy = \( 2,500 \times \frac{10}{100} = 250 \) kcal.

Question 23

As trophic level increases (e.g., from producers to primary consumers to secondary consumers, etc.), population size generally decreases. This is because of the 10% energy transfer rule: only ~10% of energy from one trophic level is available to the next. With less energy available at higher trophic levels, there's less biomass (energy storage) to support a large population. For example, in a grass → rabbit → fox food chain: grass (producers) can support many rabbits (primary consumers), but rabbits can only support a few foxes (secondary consumers) because most energy is lost (not transferred) between levels.

Question 24

The ultimate source of energy for most ecosystems is the Sun (solar energy). Producers (like plants, algae) use photosynthesis to capture solar energy and convert it into chemical energy (glucose), which then flows through the food web as organisms eat one another. Some ecosystems (e.g., deep-sea hydrothermal vents) use chemical energy from inorganic compounds, but most terrestrial and aquatic ecosystems rely on solar energy.

Question 25

Answer:

s:

1. Energy for rat: \( \boldsymbol{2,500} \) kcal; Energy for snake: \( \boldsymbol{250} \) kcal (or total \( \boldsymbol{2,750} \) kcal, depending on interpretation).
2. Population size decreases with increasing trophic level because of the 10% energy transfer rule (less energy available to support large populations).
3. The ultimate source of energy for the ecosystem is the Sun (solar energy).
4. The process is photosynthesis, performed by producers (e.g., grass, plants, autotrophs).