What group of organisms are responsible for capturing energy within ecosystems

The type of organisms that take energy by eating up other organisms in an ecosystem are called 'CONSUMERS'. Now these consumers are further divided into three major classes:

1. Primary consumers: this type of consumers feed directly from the producers (plants) and they only eat grass, leaves, vegetables, etc. Such animals are also called herbivores. Example: rabbit

2. Secondary consumers: these are the animals that eat up primary consumers (animals that feed only on plants). These animals are called carnivores. Example: snake

3. Tertiary consumers: animals that eat carnivores which eats a herbivore are called tertiary consumers. They can be completely carnivore or omnivore (who feed on animals and plants both). Example: humans (they feed on animals and plants both)

they deliver oxygen to the blood

i think its the first one