Answer:
All living organisms need to exchange substances with their environment to survive. Single-celled organisms exchange substances through their cell membrane via diffusion or endocytosis/exocytosis. Multicellular organisms have specialized organs and tissues to facilitate exchange, such as the lungs for gas exchange or the small intestine for nutrient absorption. The difference in exchange methods is due to their size and complexity. Single-celled organisms are small and have a large surface area-to-volume ratio, while multicellular organisms are larger and have a smaller surface area-to-volume ratio, making it more challenging to exchange substances efficiently through their cell membrane.
Step-by-step explanation:
All living organisms need to exchange substances with their environment to obtain nutrients, remove waste products, and regulate their internal conditions. The way in which organisms exchange substances depends on their size, complexity, and environment.
Single-celled organisms, such as bacteria and protists, exchange substances with their environment through their cell membrane. The cell membrane is selectively permeable, meaning that it only allows certain substances to pass through. Small molecules, such as oxygen, carbon dioxide, and water, can diffuse across the cell membrane to enter or leave the cell. Single-celled organisms can also engulf or excrete larger particles through processes such as endocytosis and exocytosis.
Multicellular organisms, on the other hand, have more complex systems for exchanging substances with their environment. They have specialized organs and tissues that are responsible for different functions, such as absorption, transport, and excretion. For example, the lungs in mammals are responsible for gas exchange, the small intestine absorbs nutrients from food, and the kidneys remove waste products from the blood. Multicellular organisms also have circulatory systems that transport substances, such as oxygen and nutrients, throughout the body.
The main reason why multicellular organisms and single-celled organisms exchange substances differently are due to their size and complexity. Single-celled organisms are small and have a large surface area-to-volume ratio, which allows them to exchange substances efficiently through their cell membrane. In contrast, multicellular organisms are larger and have a smaller surface area-to-volume ratio, which makes it more difficult to exchange substances efficiently through their cell membrane. Therefore, multicellular organisms have developed specialized organs and tissues to facilitate the exchange of substances with their environment. Additionally, multicellular organisms have more complex physiological processes and require more nutrients and oxygen to sustain their metabolic activity compared to single-celled organisms.