Class IX Biology - Chapter: Tissues - Topic: Plant Tissues Numerical Problems (Conceptual)

Problem 1: Calculating Cell Division Rate (Conceptual)

If a meristematic cell divides every 24 hours, and you start with one such cell, how many cells would you have after 3 days, assuming all daughter cells also divide at the same rate?

Solution:

This is a conceptual problem illustrating exponential growth due to cell division.

• After 24 hours (Day 1): 1 cell divides into 2 cells.
• After 48 hours (Day 2): Each of the 2 cells divides, resulting in 2 * 2 = 4 cells.
• After 72 hours (Day 3): Each of the 4 cells divides, resulting in 4 * 2 = 8 cells.

Alternatively, using the formula 2^n, where n is the number of divisions: Number of divisions in 3 days = 3 days * (1 division / day) = 3 divisions Number of cells = 2^3 = 8 cells

Therefore, after 3 days, you would have 8 cells.

Problem 2: Area Covered by Epidermal Cells (Conceptual)

Imagine a single layer of epidermal cells covering a leaf surface. If each epidermal cell is roughly square-shaped with sides of 20 micrometers (µm), how many such cells would be needed to cover a square area of 1 square millimeter (mm²)?

Solution:

First, convert all units to be consistent. Let's convert everything to micrometers.

• Side of one epidermal cell = 20 µm
• Area of one epidermal cell = (20 µm)^2 = 400 µm²

Now, convert 1 square millimeter to square micrometers:

• 1 mm = 1000 µm
• 1 mm² = (1000 µm) * (1000 µm) = 1,000,000 µm²

Number of cells needed = (Total area to be covered) / (Area of one cell) Number of cells needed = 1,000,000 µm² / 400 µm² = 2500 cells

Therefore, 2500 epidermal cells would be needed to cover an area of 1 square millimeter.