Question

What can affect phases/stages of growth? (a) Temperature (b) Light (c) Gravity (d) All of these

Short answer

(d) All of these

Step-by-step solution

Understanding the Factors

Firstly, realize that growth in biological organisms can be influenced by several factors.

Analyze Option (a) - Temperature

Understand that temperature can indeed affect the growth phases of plants and animals. Too high or too low temperatures can slow down or speed up growth.

Analyze Option (b) - Light

Recognize that light plays a significant role especially in plants' growth where it is required for processes like photosynthesis.

Analyze Option (c) - Gravity

Gravity is especially important in determining the orientation of growth. For example, in plants, roots grow downwards due to gravity, and shoots grow upwards.

Conclusion on the Best Option

Since all factors: temperature, light and gravity, have been shown to affect growth, the answer should be all of these.

Key concepts

Temperature and Growth

Temperature is a critical environmental factor influencing the growth stages in both plants and animals. It affects metabolic rates, which in turn can alter the pace at which organisms develop and mature. In plants, for instance, enzyme activities that are vital for growth are highly temperature-dependent. A moderate temperature range can optimize these activities, promoting healthy growth and development.

Conversely, temperatures that stray too far from an organism's optimum range can lead to stress. Extreme cold can slow down enzyme activity or even stop it altogether, while excessive heat might denature enzymes, essentially halting growth. In animals, very high or low temperatures can impact physiological functions like blood circulation and respiration, ultimately affecting their growth and survival.

Light and Photosynthesis

Light is an essential component of plant growth, primarily because it is the energy source for photosynthesis. Through photosynthesis, plants convert light energy into chemical energy, producing glucose that fuels growth and development. The intensity, quality, and duration of light can all influence the rate of photosynthesis.

Plants adapted to low-light environments may have larger leaves to capture more light, whereas those adapted to high-intensity light often have smaller, thicker leaves to prevent water loss. Without adequate light, plants may become leggy, as they stretch towards a light source, or may not produce as much chlorophyll, resulting in pale leaves. Moreover, light also regulates critical processes such as flowering through photoperiodism, which is the plant's response to the length of day or night.

Gravity and Plant Orientation

Gravity is a constant force that all living organisms have adapted to over time. In plants, gravity helps to determine the orientation of growth – a phenomenon known as gravitropism. Roots exhibit positive gravitropism, growing in the direction of gravitational pull, thus ensuring they anchor the plant and absorb water and nutrients from the soil.

Shoots and Plant Responses

On the other hand, shoots typically exhibit negative gravitropism, growing upwards and away from the earth’s gravitational pull. This orientation allows shoots to reach light for photosynthesis efficiently.

Gravitropism is guided by the plant hormone auxin, which redistributes in response to gravity, promoting differential growth rates on different sides of the root or shoot. Understanding how gravity affects plant orientation is crucial not just for agriculture and horticulture, but also for space biology research, wherein the absence of gravity poses unique challenges to plant growth.