To determine which statement is correct with respect to growth, let's analyze each option step by step.
### Step-by-Step Solution:
1. **Understanding Growth in Unicellular Organisms:**
- Unicellular organisms, such as bacteria and protozoa, primarily grow through cell division. However, this process is often considered a form of reproduction rather than growth in the traditional sense. When a unicellular organism divides, it produces two new organisms, which means that individual growth is not observed in the same way as in multicellular organisms.
- **Hint:** Consider how unicellular organisms reproduce and how that relates to growth.
2. **Growth in Plants:**
- In plants, growth occurs through cell division, particularly in specific regions known as meristems. This process continues throughout the plant's life, allowing for continuous growth.
- **Hint:** Think about where growth occurs in plants and whether it is limited to certain stages.
3. **Growth in Animals:**
- In animals, growth due to cell division occurs primarily during certain developmental stages (e.g., infancy and adolescence). After reaching maturity, the rate of growth significantly decreases, and in many cases, growth ceases altogether.
- **Hint:** Reflect on the life stages of animals and how growth varies across those stages.
4. **Cell Elongation in Unicellular Organisms:**
- Unicellular organisms do not typically exhibit growth through cell elongation; instead, they grow by increasing their cell size before dividing. However, the statement suggests that they show growth by cell elongation, which can be misleading.
- **Hint:** Consider the difference between cell division and cell elongation in the context of unicellular organisms.
5. **Evaluating the Statements:**
- **Option A:** "A unicellular organism does not grow." - This statement is misleading because unicellular organisms do grow, but their growth is not characterized in the same way as multicellular organisms.
- **Option B:** "In plants, growth by cell division does not occur throughout their lifespan." - This statement is incorrect because plant growth through cell division does occur continuously.
- **Option C:** "In animals, the growth due to cell division is seen only up to a certain stage." - This statement is correct as animal growth does slow down and eventually stop after reaching maturity.
- **Option D:** "Unicellular organisms show growth by cell elongation." - This statement is incorrect as unicellular organisms primarily grow through cell division.
### Conclusion:
The correct statement regarding growth is: **"In animals, the growth due to cell division is seen only up to a certain stage."**
