NCERT Class 6 Science — Chapter 4: The living organisms - characteristics and habitats

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What is the primary physiological function of the modified leaves (spines) in cactus plants?

Official previous-year question

Verified 1 Aug 2026.

Options

ATo provide mechanical support to the stem.
BTo facilitate photosynthesis.
CTo absorb atmospheric moisture.
DTo reduce water loss through transpiration.

Did you get this right?

Solution

Correct Option

The correct option is

To reduce water loss through transpiration.

Explanation

Cacti are xerophytes, plants adapted to survive in arid environments with limited water availability. To minimize water loss and ensure survival, these plants undergo specific morphological and physiological modifications, particularly regarding their leaves and stems.

Option Analysis

To provide mechanical support to the stem. is incorrect: Mechanical support in plants is typically provided by woody stems, collenchyma, and sclerenchyma tissues. While spines are hard and sclerified, their primary role is defense against herbivores rather than structural support for the stem.
To absorb atmospheric moisture. is incorrect: The absorption of water and mineral nutrients is the primary function of the root system. While some specialized plants (like epiphytes) absorb moisture through aerial roots or leaves, cactus spines do not perform this function.
To reduce water loss through transpiration. is correct: In cacti, leaves are modified into hard, pointed structures called spines. This modification significantly reduces the surface area exposed to the sun and wind, thereby minimizing water loss through transpiration. Additionally, spines provide shade to the stem and protect the plant from grazing animals.
To facilitate photosynthesis. is incorrect: Since the leaves are modified into spines, they lack chlorophyll and cannot perform photosynthesis. Consequently, the function of photosynthesis is taken over by the flattened or cylindrical green stem, known as a phylloclade.

Key Takeaway

Spines in xerophytic plants are modified leaves designed to reduce the surface area for transpiration, thereby conserving water, while the green stem (phylloclade) assumes the function of photosynthesis.

Your note

More from Chapter 4: The living organisms - characteristics and habitats

With reference to the concept of 'adaptation' in living organisms, consider the following statements: 1. It refers to the small changes that take place in the body of a single organism over a short period to overcome changes in the surroundings. 2. It involves specific features or habits that enable an organism to live naturally in a place. 3. It is a rapid process that occurs within a few days. Which of the statements given above is/are correct?

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What does the term 'acclimatisation' refer to in a biological context?

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Consider the following statements regarding the components of a habitat: 1. The organisms, both plants and animals, living in a habitat constitute its biotic components. 2. Rocks and soil are considered biotic components of a habitat. 3. Sunlight and heat are classified as abiotic components of a habitat. Which of the statements given above is/are correct?

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With reference to the germination of seeds, consider the following statements based on abiotic factors: 1. Seeds can germinate in the complete absence of air and water. 2. Light and heat are abiotic factors that influence the growth of plants. 3. Abiotic factors are important for all living organisms. Which of the statements given above are correct?

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Consider the following specific features of a camel that help it survive in desert conditions: 1. They excrete a small amount of urine to conserve water. 2. They sweat profusely to keep their bodies cool. 3. They have very short legs to keep their bodies close to the ground. Which of the statements given above is/are correct?

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Correct Option

The correct option is

To reduce water loss through transpiration.

Explanation

Option Analysis

To provide mechanical support to the stem. is incorrect: Mechanical support in plants is typically provided by woody stems, collenchyma, and sclerenchyma tissues. While spines are hard and sclerified, their primary role is defense against herbivores rather than structural support for the stem.
To absorb atmospheric moisture. is incorrect: The absorption of water and mineral nutrients is the primary function of the root system. While some specialized plants (like epiphytes) absorb moisture through aerial roots or leaves, cactus spines do not perform this function.
To reduce water loss through transpiration. is correct: In cacti, leaves are modified into hard, pointed structures called spines. This modification significantly reduces the surface area exposed to the sun and wind, thereby minimizing water loss through transpiration. Additionally, spines provide shade to the stem and protect the plant from grazing animals.
To facilitate photosynthesis. is incorrect: Since the leaves are modified into spines, they lack chlorophyll and cannot perform photosynthesis. Consequently, the function of photosynthesis is taken over by the flattened or cylindrical green stem, known as a phylloclade.