DESCRIPTION OF INTERACTIVE

Factors Affecting Plant Growth

Light

This is a diagram of the the visible light spectrum in graph form. The title along the top reads ‘Example of Spectral Distribution of Sunlight’. The x-axis of the graph is labelled ‘Wavelength (nm)’ and shows a scale increasing by 100 from 380 to 780. To the left of the graph is written ‘Ultra-violet’ and to the right is written ‘Infrared.’ The centre portion of the graph is labelled ‘Visible light. This section shows a series of peaks along the top, and shows shades of (from left to right) purple, blue, green, yellow, orange, and red.
The relative amounts of each wavelength of light in the spectrum of visible sunlight.

The light that reaches the Earth from the Sun covers many wavelengths. It is from the visible light spectrum, which covers from 380 nm to 780 nm, that plants use in photosynthesis. SBI4U will describe the light requirements and light capturing systems of plants in greater detail. Special grow lights that cover the visible light spectrum are therefore the best for indoor plant growth.

Photoperiodism(definition:The response of an organism to seasonal changes in day length.) describes a plant’s response to changes in light at different times of the day.

Seasonal changes as well as different geographical locations also impact the light available for plants. It is these changes in light intensity and length of exposure that dictate the growing season in Ontario and initiate the change in colour of the leaves in the fall.

Check the Extension box below this interactive to see more about why leaves change colour in the Fall!

Temperature

This is an image of a clump of squash plants in dry, brown soil. The sun is shining and the leaves of the plants are all wilted.
Squash plants wilting during the heat of the day.

Temperature has a great influence on plant growth and development. Many flowers will bloom only at a specific temperature, which is thought to correspond to the arrival of insect pollinators. Certain seeds, including many pine species, will only germinate after they have been through a cold cycle.

The opening and closing of stomata on the leaves is also influenced by the temperature. Most cellular process have an optimal temperature, and a stoma will open up when that temperature is right for cellular respiration to allow the gas exchange needed by the process. This also has an impact on transpiration. When the stomata are open, water is released into the atmosphere, which then pulls water up from the soil to replace it. If the soil is dry and not enough water is available to replace the lost water from transpiration, the plant will wilt.

Some plants respond directly to temperature changes. These plants will curl up their leaves when the temperature drops. You will learn more about this and other plant responses to stimuli later in this activity.

Soil

This is an image of two hands held together holding dark soil. The background is more of the same dark soil. In the middle of the clump of soil in the hands is a small plant with four green leaves.
Rich, dark soil contains lots of organic nutrients.

Soil plays a number of roles in plant growth and development. It is the medium in which plants anchor themselves, so the soil type needs to fit the root type of the plant. If the soil is too compacted, apical root tips may not be able to drive through it.

Retention of water is also an important soil characteristic. Sandy soil will drain quickly, while soil that has a high clay content may hold too much water, causing the roots to rot. Water is obviously needed by the plant for photosynthesis, but it also carries dissolved nutrients needed by the plant.

For the water to carry nutrients, the nutrients must be there in the first place! Soils high in organic material have high nutrient content, insuring that the plant has all that it needs to support healthy growth. For plants, these nutrients include a variety of mineral ions as they can produce most of the other macromolecules and vitamins they need on their own.

Soil acidity is also crucial to plant health. The pH of the soil will impact how readily the nutrients will dissolve into the water contained in the soil. For most nutrients, a slightly acidic pH is optimum for tissue growth and differentiation.

Nutrients

This is an image of a black containing of ‘Promix’ multi-purpose garden fertilizer. The container has flowers and vegetables on the top-right corner. The ‘Promix’ label is written vertically along the left side. The writing in the centre is is English and French. At the bottom of the container is ‘20-8-8.’
Fertilizer comes in many different mixtures.

Ever wonder what those numbers are on a bag of fertilizer? The three numbers represent the percentage of nitrogen (N), phosphorus (P), and potassium (K). For fertilizer labelled as 20 - 8 - 8, it means that 20% of the mixture is N, 8% is P, and 8% is K. The rest of the material is filler to cut the concentration of the nutrients.

Unlike what's required for animals, N, P, and K are the main inorganic macronutrients(definition:A substance required in relatively large amounts by living organisms.) for plants, which means they are needed in relatively large quantities. Others include magnesium (Mg), calcium (Ca) and sulfur (S). Micronutrients(definition:A chemical element or substance required in trace amounts for the normal growth and development of living organisms.) are also needed by the plant, only in much smaller amounts. Micronutrients include copper (Cu), iron (Fe), and zinc (Zn).