Why do the leaves fall in the fall, but the back side up

Back side up.

This is because the front cells of the leaves are neatly arranged and dense, containing a lot of chloroplasts. On the back of the leaf, there are few chloroplasts in the cell tissue, and the arrangement is loose and cavitary, so it is lighter than the front.

The leaves are heavy on the front and light on the back, so when the leaves fall to the ground, they are usually the back up and the front down.

Leaf shape: 1. Oval: shaped like an oval, the widest in the middle, and round at the tip and base, such as the leaves of camphor trees, rubber trees, tea trees, black date trees, and primroses.

2. Heart-shaped: shaped like a heart, the base is wide and round and slightly concave, such as the leaves of sweet potato, morning glory, bauhinia, and hemp. If it is inverted in the shape of a heart, it is called an inverted heart, like the leaflets of sorrel.

3. Lanceolate: also called lanceolate, the leaf base is wider, the apex is thin, and the length is about 3-4 times the width, such as the leaves of peach, willow and bamboo, if it is lanceolate inverted, it is called inverted lanceolate, such as the leaves of small tillers.

4. Round: shaped like a disc, nearly equal in length and width, such as, nasturtium leaves.

Most of the deciduous leaves of plants are caused by the special internal structure of the leaves, which is caused by the back of the leaves and the leaf side down. In most plants, there is a significant difference in the amount of sunlight found in the leaves, the back of the leaf and the surface of the leaf during the growth of the plant, resulting in a difference in the structure of the two sides of the leaf.

The cells that are usually close to the leaf surface are rectangular and regularly arranged and are called palisade tissues; The cells near the dorsal surface of the leaf are irregular lumps called spongy tissue. The fence is tightly organized and contains a large amount of chlorophyll, which is mainly used to receive light energy and use carbon dioxide in the air to produce a large amount of organic matter, with a high density.

The sponge tissue is loosely arranged and has less chlorophyll, which is mainly used to store internal products and water in plants, and has a low density. Therefore, not only is the color of the leaf surface usually brighter than the back of the leaf, but it is also heavier, and when the leaf falls, the heavier side will face downward, and the back of the leaf will face up.

The leaves will fall because autumn is coming, due to the shortening of the sunshine and the decrease in temperature, the water ** is insufficient, and the abscisic acid in the plant will be produced in large quantities, in order to reduce the transpiration of water, the trees can get rid of the leaves of the whole body in the autumn to survive the winter safely. This is a normal physiological phenomenon of trees, and it is also an adaptation of trees to adverse climatic conditions such as low temperature and drought.

Leaves are the part of the tree that undergoes photosynthesis, and the leaves can come in a variety of shapes, sizes, colors, and textures. The leaves can be clustered together or scattered all over the place. The edges of the leaves can be smooth or jagged.

Leaf support – protects young leaves. Some plants do not have a leaf support, and some plants have a leaf that falls off very early.

Leaves are the main organs of plants for photosynthesis and nutrient production. By absorbing carbon dioxide, oxygen is released (release place: stomata), food is provided, and shelter from the wind and rain. Leaf photosynthesis is done through chloroplasts.

Falling leaves in autumn is a self-protection mechanism for plants. Cold winter is coming, and evergreen leaves have thicker wax and resin on them to protect them from freezing and cracking, but deciduous trees with thinner leaves are not very resistant to cold climates. Because water swells when frozen, leaf cells that contain water are prone to cracking during the winter months, causing them to be unable to photosynthesize.

If these leaves don't fall, they won't be able to provide nutrients to the tree in the winter, and they can be harmful to the tree – too many and too thick leaves can make the tree easy to be blown down by the wind, and if there is snow on the leaves, it can also break the tree. In addition, insect infestation from these leaves can also damage the entire tree.

Interestingly, the fallen leaves are not simply blown off from being blown by the wind, but are tightly controlled by the tree's conditioning system. As daylight hours shorten and temperatures gradually decrease, hormones within plants are activated and stimulate the process of leaf shedding

Chlorophyll stops being produced and the pigment begins to break down, causing the leaves to turn yellow;

The pipes through which plants transport water to leaves and nutrients from leaves to plants are closed;

Between the petioles and branches, cells called exfoliation begin to grow, which act like a knife and slowly cut through the leaves and trunk without leaving an open wound.

After the leaves fall off, the plant goes into dormancy, building up energy for the big buds of spring.

The reason why the leaves fall off in autumn is because their moisture and climate temperature are affected, so some deciduous trees will lose their leaves in autumn.

The law of nature, everything has a law, spring germinates, autumn bears fruit. In late autumn, when the weather turns colder, it will gradually become boring and the leaves will fall. This is reincarnation.

When formed, the slightest breeze blows and the leaves fall. Defoliation is a skill of broad-leaved trees in temperate regions to reduce transpiration and prepare for a safe winter. Defoliation also has a lot to do with the abscisic acid contained in the tree.

After reading the explanation, let's talk about the fallen leaves in the south. In the south, the leaves fall not in autumn, but in.

1. The autumn wind blows, and the leaves fall one after another, like beautiful butterflies dancing.

2. A gust of autumn wind blows, and the leaves fall down like snowflakes.

3. A gust of autumn wind blows, and the leaves fall like butterflies.

4. A gust of autumn wind blew, and the leaves fell down like a small butterfly and a silver butterfly flew down.

5. A gust of autumn wind blows, and the leaves slowly drift down, like golden butterflies dancing.

Common deciduous plants include metasequoia, ginkgo, golden pine, weeping willow, maple poplar, zelkova, oak tree, mulberry, fig, barberry, magnolia, plum, mountain plum, sweetgum and so on.

Deciduous plants, a common noun in botany, are opposed to evergreen plants, where there is a time of year when the leaves will fall off completely, and the branches will become bare and leafless. The causes of defoliation are clearly related to the season and climate. As the temperature is generally lower in autumn and winter, the climate is drier and more prone to water shortage, resulting in the cessation of plant growth, the loss of all leaves, and the emergence of young leaves in the following year.

Fall:

Autumn is one of the four seasons of "Spring, Summer, Autumn and Winter". In China, the "beginning of autumn" of the 24 solar terms is traditionally used as the starting point of autumn. Autumn means that rainfall, humidity, etc. tend to drop or decrease, and everything in nature begins to grow from lush to mature.

According to the modern scholar Zhang Baokun's average temperature, the average temperature is divided into four seasons, and the index is that the period when the average temperature is lower than 10 is winter, the period higher than 22 is summer, and the period of 10 22 is spring and autumn.

The mesophyll of the leaves is divided into two layers, the upper layer is palisade tissue, and the cells are closely arranged, and the lower layer is sponge tissue, and the cells are loosely arranged, so the upper layer of the leaves is heavier than the lower layer, so when the leaves fall, the heavier upper layer is facing down, and the lighter lower layer is facing up, so the leaves fall and the back side is facing up.

The reasons why leaves fall in autumn are as follows:

Leaves are in trees and their main function is to produce "food". Plants, like animals, need to consume sugar to maintain physiological functions. It's just that there is a difference between the two, animals rely on eating, while plants rely on photosynthesis.

The fall of leaves is generally divided into two situations, one is that the leaves are already dead. Plants, like animals, are born, old, sick and die, and the other is a man-made "accident", such as a passerby picking off a leaf. Dead leaves have no physiological function and have to fall to dust.

The other is caused by the environment, and there are also two reasons for this: man-made and natural. In short, man-made is something man-made, such as a factory next to a tree or a nuclear power plant accident.

Leaves will choose to "actively fall in the face of adversity" to protect themselves. Natural environmental reasons are the most common situation, and the temperature drops sharply in autumn and winter, so it is impossible to carry out physiological activities, so it is necessary to hibernate people.

It is well known that leaves can absorb light energy through photosynthesis in a suitable climate, and combine carbon dioxide and water from the air into organic matter needed for tree growth, while releasing oxygen. However, with the attack of cold air, the temperature and rain begin to drop in autumn, the daylight hours begin to shorten, and the photosynthesis of the leaves does not play a big role.

As the temperature drops, the stems have thickened bark, the roots are buried under the soil, and the thin leaves are left to fight alone. The impending cold also made these leaves, which were originally born for photosynthesis, at a loss.

The drop in temperature and the decrease in precipitation have directly made the process of not simply absorbing water "worse". There are many stomata on the leaves, and the tree loses a lot of water as it breathes. The leaves had no choice but to abandon them.