Question

is happening to dečiduous trees oHly ot tc ccglC all at once. Plants do not just decide to drop leaves; it is a process of changing their physiology - it involves hormones, and some changes must be made to protect the plant from damage. DUL IIO In three paragraphs, answer the following questions. I expect you to look up the answers! 1. What processes are responsible for the change in color of leaves in the fall? There are two. 2. Why do some trees drop their leaves and others do not? Give an ecological explanation. 3. What actually happens physically to the leaves that causes them to drop off of the branch?

Answer 1

1) Change of color in the leaf in the fall

In the fall, because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process. The chlorophyll breaks down, the green color disappears, and the yellow to orange colors become visible and give the leaves part of their fall splendor.

It takes a lot of energy to make chlorophyll. If the plants break down the chlorophyll and move it out of their leaves before the leaves fall, plants save energy. The plants can reabsorb the molecules that make up chlorophyll. Then, when it's warm and sunny enough to grow again, the plants can use those molecules to remake the chlorophyll. That way the plants don't have to make chlorophyll from scratch.

There are other pigments in leaves called carotenoids. Carotenoids are yellow and orange. Anthocyanins are other plant pigments that are only made in the fall. These pigments cause red, pink, or purple colors. Anthocyanins also protect leaves from being eaten or getting sun burned.

2) Ecological Explanation

Trees lose their leaves as a protection against environmental stress.
In the tropical and sub-tropical areas, winter weather is not a challenge for the trees, so they don't drop their leaves all at once, instead they can keep up the process of photosynthesis all year.

Leaves drop for many reasons, including environmental stress, pests and disease.

Shock – Shock from transplanting, repotting or dividing, is probably the number one reason for leaf loss in plants. Fluctuations in temperature, light, and moisture can have an adverse effect on plants.

Weather and Climate – As with environmental changes that can lead to shock, weather and climate play a huge role in causing leaves to fall, temperatures can greatly affect plants. A sudden change in temperature, be it cold or hot, can lead to foliage turning yellow or brown and dropping off.

Wet or Dry Conditions – Many plants will drop their leaves as a result of overly wet or dry conditions, overwatering commonly results in leaf yellowing and the dropping of foliage. Dry, compacted soil can have the same outcome, as roots become restricted. To conserve water in dry conditions, plants will oftentimes shed their foliage. Overcrowded container plants may drop leaves for the same reason, giving a good indication that repotting is necessary.

Seasonal Changes – The changing of the seasons can lead to the loss of leaves. Most of us are familiar with leaf loss in fall, It is not uncommon for some plants, like broad-leaf evergreens and trees, to shed their oldest leaves in spring to make room for regrowth of new, young leaf tips. Others do this in late or early fall.

Pests and Disease – Finally, certain pests and disease can occasionally cause leaf drop. Therefore, you should always examine the leaves carefully for any signs of infestation or infection whenever your plant is losing leaves.

3) physically reason why leaves drop off the trees

Once chlorophyll production stops, it gets broken down and taken back into the tree. This layer stops the transport of nutrients and water to the leaf and becomes the main physical reason trees lose their leaves. The abscission layer also helps protect this sensitive area of the plant from winter cold and dryness.

Leaves fall off trees so that the trees can survive the winter.