Short Answer
Chloroplasts are absent in animal cells because animals cannot prepare their own food. Chloroplasts are required for photosynthesis, a process that only green plants and some algae can perform.
Animals depend on plants or other animals for food. Since animals do not perform photosynthesis, they do not need chloroplasts in their cells.
Detailed Explanation :
Absence of Chloroplasts in Animal Cells
- Chloroplasts are organs of photosynthesis.
- Animal cells do not perform photosynthesis.
Chloroplasts are special cell organelles that help in the process of photosynthesis. Photosynthesis is the process by which green plants prepare their own food using sunlight, carbon dioxide, and water. This process takes place only in cells that contain chlorophyll, which is present inside chloroplasts.
Animal cells do not contain chlorophyll and therefore cannot carry out photosynthesis. Because chloroplasts are only useful for photosynthesis, animal cells do not require them. Hence, chloroplasts are completely absent in animal cells.
Difference in Mode of Nutrition
- Plants are autotrophic.
- Animals are heterotrophic.
One of the main reasons for the absence of chloroplasts in animal cells is the difference in mode of nutrition.
Plants are autotrophs, which means they make their own food by photosynthesis. For this purpose, they require chloroplasts.
Animals are heterotrophs, which means they cannot make their own food. They obtain food by eating plants or other animals. Since animals depend on external sources of food, there is no need for photosynthesis in animal cells, and therefore no need for chloroplasts.
Role of Chlorophyll
- Chlorophyll traps sunlight.
- Animal cells lack chlorophyll.
Chlorophyll is a green pigment found inside chloroplasts. It absorbs sunlight and provides energy for photosynthesis. Without chlorophyll, photosynthesis cannot occur.
Animal cells do not contain chlorophyll. Because chlorophyll is absent, chloroplasts are also unnecessary in animal cells.
Energy Requirement in Animals
- Animals obtain energy from food.
- Mitochondria release energy.
Animals obtain energy by breaking down food through respiration. This process occurs in mitochondria, which are present in both plant and animal cells.
Since animals get ready-made food and use mitochondria to release energy, they do not require chloroplasts to make food. Thus, mitochondria fulfill the energy needs of animal cells, not chloroplasts.
Lifestyle and Movement
- Plants are fixed in one place.
- Animals can move freely.
Plants are fixed organisms and cannot move from one place to another in search of food. Therefore, they must produce their own food wherever they are, which is why chloroplasts are necessary.
Animals can move freely and search for food. Because of this ability, animals do not need to make their own food and hence do not require chloroplasts.
Cell Structure Differences
- Plant cells have chloroplasts and cell walls.
- Animal cells lack chloroplasts and cell walls.
Plant cells have special structures like chloroplasts and cell walls that support photosynthesis and provide rigidity.
Animal cells do not need these structures because their functions and lifestyle are different. Animal cells are adapted for movement, digestion, and coordination rather than food production.
Evolutionary Reason
- Chloroplasts evolved in plant cells.
- Animals evolved different survival methods.
From an evolutionary point of view, plants developed chloroplasts to survive independently by making their own food. Animals evolved different systems such as digestive systems and sensory organs to obtain food from the environment.
Therefore, chloroplasts became a permanent feature of plant cells but were never required in animal cells.
Dependence on Plants
- Animals depend on plants for food.
- Energy originates from photosynthesis.
Although animals do not have chloroplasts, they indirectly depend on photosynthesis. Plants produce food and oxygen through chloroplasts, which animals use for survival.
Thus, chloroplasts are essential for life on Earth, but only plant cells need to contain them.
Importance of Chloroplast Absence
- Makes animal cells simpler.
- Allows specialization for other functions.
The absence of chloroplasts allows animal cells to specialize in other functions such as movement, digestion, nerve transmission, and reproduction. This specialization helps animals adapt better to their environment.
Conclusion
Chloroplasts are absent in animal cells because animals do not perform photosynthesis and cannot make their own food. Animals are heterotrophic and depend on plants or other animals for nutrition. Since chlorophyll is absent in animal cells and energy is obtained through respiration in mitochondria, chloroplasts are not required. Therefore, the absence of chloroplasts in animal cells is due to differences in nutrition, lifestyle, structure, and function between plants and animals.