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Tissues - Tissues for Growth in Plants

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Meristematic tissues are the primary tissues responsible for growth in plants due to their continuous capacity for cell division.

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Cells of meristematic tissue are characterized by very active metabolism, dense cytoplasm, thin cellulose walls, and prominent nuclei. They typically lack vacuoles because they do not need to store food or waste products.

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Apical Meristem: Located at the growing tips of stems and roots. It is responsible for the increase in the length of the plant (primary growth).

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Intercalary Meristem: Located at the base of leaves or internodes (on either side of the node). It helps in the elongation of the internodes and leaves.

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Lateral Meristem (Cambium): Located on the lateral sides of the stem and root. It is responsible for increasing the girth or thickness of the plant (secondary growth).

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Growth in plants is localized to specific regions containing these tissues, unlike animals where growth is more uniform.

📐Formulae

Growth Rate=L2−L1t2−t1\text{Growth Rate} = \frac{L_2 - L_1}{t_2 - t_1}

Primary Growth∝Activity of Apical Meristem\text{Primary Growth} \propto \text{Activity of Apical Meristem}

Secondary Growth (Girth)∝Activity of Lateral Meristem\text{Secondary Growth (Girth)} \propto \text{Activity of Lateral Meristem}

💡Examples

Problem 1:

A plant height increased from 10 cm10\text{ cm} to 25 cm25\text{ cm} over a period of 30 days30\text{ days}. Calculate the average growth rate per day and identify the tissue responsible for this increase.

Solution:

Growth Rate=25−1030=1530=0.5 cm/day\text{Growth Rate} = \frac{25 - 10}{30} = \frac{15}{30} = 0.5\text{ cm/day}

Explanation:

The average growth rate is 0.5 cm/day0.5\text{ cm/day}. The tissue responsible for the increase in the length of the plant is the Apical Meristem.

Problem 2:

Why do meristematic cells lack vacuoles, whereas mature plant cells have large central vacuoles?

Solution:

Vacuole Presence≈0% in Meristems\text{Vacuole Presence} \approx 0\% \text{ in Meristems}

Explanation:

Meristematic cells are constantly dividing and are metabolically very active. They do not need to store nutrients or provide structural support (turgidity) like mature cells do. Therefore, they lack vacuoles to maintain a dense cytoplasm for rapid division.

Problem 3:

If the girth of a tree trunk increases by 2 cm2\text{ cm} every year, how much will the girth increase over 5 years5\text{ years}? Which tissue is involved?

Solution:

2 cm×510 cm\begin{array}{r} 2 \text{ cm} \\ \times 5 \\ \hline 10 \text{ cm} \end{array}

Explanation:

The total increase in girth is 10 cm10\text{ cm}. The tissue responsible for increasing the thickness (girth) of the plant is the Lateral Meristem (also known as the cambium).