14.5

Tropic responses

10 flashcards to master Tropic responses

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Definition Flip

Define gravitropism.

Answer Flip

Gravitropism is a plant's growth response to gravity. Roots show positive gravitropism (grow downwards), while shoots show negative gravitropism (grow upwards).

Example: A seed germinating underground sends its shoot up and root down.
Definition Flip

Define phototropism.

Answer Flip

Phototropism is a plant's growth response to a light source. Shoots show positive phototropism (grow towards light), while roots usually show negative phototropism (grow away from light).

Example: A plant on a windowsill bends towards the sunlight.
Key Concept Flip

How would you investigate phototropism in shoots?

Answer Flip

Place several seedlings in a box with a hole on one side, allowing light to enter from that direction. Observe the shoots bending towards the light source over a few days. Use a control group in normal light conditions for comparison.

Key Concept Flip

How would you investigate gravitropism in shoots and roots?

Answer Flip

Place germinating seeds horizontally on moist filter paper in a Petri dish. Observe the roots growing downwards (positive gravitropism) and the shoots growing upwards (negative gravitropism). Keep one set upright as a control.

Key Concept Flip

Where is auxin produced in a plant?

Answer Flip

Auxin is primarily produced in the shoot tip (apical bud) of a plant. From there, it diffuses to other parts of the plant, influencing growth.

Example: Removing the shoot tip reduces auxin and lateral bud growth.
Key Concept Flip

How does auxin travel through the plant?

Answer Flip

Auxin diffuses from the shoot tip through the plant tissues. The distribution of auxin is influenced by factors like light and gravity, leading to uneven growth.

Example: Auxin moves down the shaded side of a shoot.
Key Concept Flip

How does light affect the distribution of auxin in a shoot?

Answer Flip

Light causes auxin to concentrate on the shaded side of a shoot. This unequal distribution causes cells on the shaded side to elongate more, resulting in the shoot bending towards the light.

Example: The stem of *Arabidopsis thaliana* bends towards light due to increased auxin on the shaded side.
Key Concept Flip

How does gravity affect the distribution of auxin in a horizontal shoot?

Answer Flip

Gravity causes auxin to accumulate on the lower side of a horizontal shoot. The higher concentration of auxin on the lower side stimulates cell elongation, causing the shoot to bend upwards (negative gravitropism).

Example: A bent tomato plant stem turning upwards.
Key Concept Flip

What is the role of auxin in shoot growth?

Answer Flip

Auxin promotes cell elongation in shoots. Higher concentrations of auxin stimulate cell elongation, leading to growth towards a stimulus (light or against gravity).

Example: Increased auxin in coleoptiles bending towards light.
Key Concept Flip

What happens to root growth in response to high concentrations of auxin?

Answer Flip

High concentrations of auxin inhibit root growth. While auxin promotes cell elongation in shoots, it has the opposite effect in roots at higher concentrations.

Example: If a root is placed horizontally, auxin accumulates on the lower side slowing the growth which allows the upper side to grow faster, making the root bend down.

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14.4 Homeostasis 15.1 Drugs

Key Questions: Tropic responses

Define gravitropism.

Gravitropism is a plant's growth response to gravity. Roots show positive gravitropism (grow downwards), while shoots show negative gravitropism (grow upwards).

Example: A seed germinating underground sends its shoot up and root down.
Define phototropism.

Phototropism is a plant's growth response to a light source. Shoots show positive phototropism (grow towards light), while roots usually show negative phototropism (grow away from light).

Example: A plant on a windowsill bends towards the sunlight.

About Tropic responses (14.5)

These 10 flashcards cover everything you need to know about Tropic responses for your Cambridge IGCSE Biology (0610) exam. Each card is designed based on the official syllabus requirements.

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