(2) Cell wall contains cellulose: the outer layer is pectin, which is sticky and slippery; The inner layer is cellulose;
(3) Cells contain chlorophyll or other pigments, which can be used for photosynthesis;
(4) Most species have flagella in some unicellular periods in their life history-highly dependent on water environment.
2. Classification: There are about 7 phyla and 25,000 species of algae, most of which are born in seawater and fresh water, and a few are born on land. 1. General characteristics
(1) cells are prokaryotic cells, with no nucleus and only ribosomes in organelles.
(2) Filaments are usually single-row cells with loose connections between cells; The filamentous weight group is block or sheet.
(3) Photosynthetic pigments are chlorophyll a and phycocyanin, so plants are blue. The storage material of photosynthetic products is mainly cyanobacteria starch.
(4) No sexual reproduction. Division reproduction is carried out by dividing cells into two parts, or vegetative reproduction is carried out by breaking filaments.
2. Classify and represent plants
At present, there are about 1500 species of Cyanophyta found and recorded, with only one class, namely cyanophyta, and three orders, namely Chromococcales, Cyanophyta and Lycophyta.
Nostoc commune) P 184
Nostoc commune belongs to trematoda.
Branchless filaments composed of single rows of cells are called algal filaments. Many algae filaments are assembled into sheet and spherical groups with male colloid sheaths. There are idioblast on the filaments, which are larger than other cells and often break here for vegetative propagation. In winter, some cells become thick-walled spores (thick-walled spores) and germinate into new filaments after dormancy.
Common Nostoc commune and Nostoc commune are edible.
Nostoc commune in the ocean can form a red tide. 1. General characteristics
The cells of green algae plants contain the same photosynthetic pigments as higher plant cells, namely chlorophyll a, chlorophyll b, lutein and carotene, so they are all green. The stored nutrients are the same, including starch and oil.
It has cell wall components similar to those of higher plants.
Swimming cells have two or four terminal flagella of equal length. Green algae plants have single cells, colonies and filaments.
There are asexual reproduction and sexual reproduction.
It is widely distributed, mainly in fresh water, common in running water and still water, wet places on land and seawater.
2. Classify and represent plants
There are about 430 genera and 6700 species of Chlorophyta, which are usually divided into Chlorophyta and Chlorophyta.
(1) Chlamydia belongs to Chlorophyta.
There are more than 100 species of Chlamydomonas, which live in fresh water ditches and ponds rich in organic matter. When they breed in early spring and late autumn, they often form large communities and turn the water green.
This plant is a single cell, oval with a nucleus and a cup-shaped chloroplast. There is a starch nucleus in chloroplast, and there are two flagella of equal length at the front of the cell. There are two contraction vacuoles at the base of the flagella, and there is 1 red eye spot beside it.
Chlamydomonas has both asexual and sexual reproduction. Asexual reproduction usually takes place at night. In the process of reproduction, algae usually stay still, and flagella shrinks or falls off to become swimming sporangia. The nucleus divides into four subnuclei first, and some species divide 3-4 times to form 8- 16 subnuclei, and then the cytoplasm divides longitudinally to form 2, 4, 8 or 16 daughter protoplasts. Each daughter protoplast secretes a cell wall and produces two flagella. Sexual reproduction is carried out after several generations of asexual reproduction. In the process of reproduction, protoplasts in cells divide into 8=64 small cells, which are called gametes. Gametes are not much different from zoospores in morphology, but smaller than zoospores. After the mature gametes are released from the mother cells, they will soon swim, that is, they will form a diploid zygote with four flagella and swim. After swimming for several hours, the zygote becomes round, the flagella falls off, and it secretes to form a thick-walled zygote with thorns on the zygote wall. After dormancy, the zygote undergoes internal meiosis when the environment is suitable, resulting in four haploid protoplasts. After the zygote wall is broken, haploid protoplasts are released, flagella is produced within a few minutes, and new individuals develop.
Sexual reproduction in most species is gamete fusion, that is, two gametes are similar in shape and the same in size.
Some of them are mixed marriages.
Some are ovulating and reproducing.
From the life history of different Chlamydomonas, it can be seen that sexual reproduction originated from asexual reproduction, and sexual reproduction developed from syngamy to heterogamy, and then to egg reproduction.
(2) Spirogyra belongs to Chlorophyta.
There are about 300 species of this genus, all of which are produced in fresh water. They are common freshwater green algae, commonly found in rivers, ponds, ditches or paddy fields. When in full bloom, large pieces are born at the bottom of the water or float on the water surface, and they feel sticky when touched by hands.
Plants are unbranched filaments connected by long cylindrical cells. There are one or several banded chloroplasts in each cell, which are spirally arranged around the protoplast and have a row of starch nuclei on it. There is a nucleus and a big vacuole in the cell. There is colloid outside the cell wall, and the tentacles are slippery.
The vegetative propagation of Spirogyra can be carried out by dividing filaments in two or dividing each cell of filaments. Spirogyra did not reproduce asexually. Sexual reproduction is conjugation, which occurs mostly in spring or autumn. In the process of reproduction, the two filaments approach each other equally, protrude from each other on the opposite sides of the two cells, and the protruding parts gradually extend and contact, so the contacted walls disappear and connect into a tube, which is called a connecting tube. Multiple rows of connecting tubes can be formed between two filaments, which looks very similar to a ladder and is called "trapezoidal connection". Protoplasts in cells contract to form gametes, and the gametes in one filament move in an amoeba-like manner, move to the opposite cell in the second filament through the connecting tube, and combine with the gametes in the cells. After the combination, the cell of the first silk has only one empty wall, and this silk is male; After the cells of the second silk are combined, each cell has a zygote, and this silk is female. When gametes fuse, the cytoplasm fuses first, and then the two nuclei fuse into a zygote. In addition, there are side joints. The zygote is drought-tolerant and will not die after withering in water. It will germinate when the environment is suitable, usually a few weeks or months after zygote formation, or even a year later, thus growing into a new plant.
(3) Charophyta belongs to Charophyta.
Charophytes are mostly found in fresh water, mostly in still water or stagnant bottom, and a few in brackish water. Plants are erect, with wheel-shaped branches and their surfaces often contain calcium. Rhizomes with single row of cell branches are fixed in sediment, and the main branches are divided into "nodes" and "internodes". There is a large cell in the center of the internode, and the periphery is composed of long cells. There are short villages around the festival, and the short branches are called "leaves"; Leaves also have "nodes" and "internodes" No matter the main branch or short branch, there is a hemispherical cell at the top, which is called api-calcell. The growth of plants is formed by the continuous division of apical cells, and the main branches can grow indefinitely; Short branches stop growing when they grow to a certain extent.
The sexual reproduction of Charophyta is egg reproduction. Female reproductive organs are called oogonia and male reproductive organs are called spermatogonia. Both male and female reproductive organs are born on the nodes of short branches. The oocyst is born on the spinous body, oblong and contains a wolf cell; Sperm sacs are born under the spines that produce sperm. Sperm is slender and spiral, and the two flagella at its front end are dragged to its back end, and the mature sperm is released into the water. When the oocysts mature, sperm enter the oocysts and combine with the eggs. The zygote secretes to form a thick wall, leaves the algae body, and germinates through meiosis after dormancy, and several charophytes can grow.
The asexual reproduction of Charophyta: one is that the broken algae sink into the water to grow "false roots" and "buds" and become new plants; The other is that beads grow at the base of algae, which contains a lot of starch, much like the roots or tubers of seed plants.
The plants of Charophyta are highly evolved, and their reproductive organs are complex in structure, surrounded by a layer of vegetative cells, which can be compared with the sexual organs of higher plants. Therefore, some people list them as independent doors.
In addition to the above-mentioned green algae, Chlorella is a common green algae. These plants are floating unicellular plants, round or oval, with thin and uniform cell walls. Chlorococcus is a unicellular plant with round and thin walls when it is young. The cell has a large chloroplast, a starch nucleus and a nucleus. Scenedesmus, the plant body is a ball, the cells are spindle-shaped or long cylindrical, and they are horizontally connected in a row; There is also Volqox (figure) and so on. In addition, the life history of Ulva lactuca has also appeared isomorphic generation alternation. Green algae and higher plants have many similarities, they have the same pigment, the product of photosynthesis is starch, and the flagella type is tail whip type. Therefore, most scholars admit that the ancestor of higher plants is green algae. Chlorophyta plays an important role in the phylogeny of plant kingdom. However, there is no clear answer as to which kind of higher green algae plants developed from. 1. General characteristics
Almost all brown algae are seafood. The algae body contains chlorophyll a, chlorophyll c, carotene and lutein. Among them, carotene and lutein are rich, so they are often yellowish brown. The stored nutrients are mainly brown algae starch (kelp sugar, a water-soluble polysaccharide) and mannitol.
Brown algae is a multicellular plant with large ribbon or branched filaments. Some plants are very big, such as giant algae, which can be as long as 400 meters. Plants are divided into three parts: ribbon, stem and rhizome.
All brown algae have sexual reproduction, including syngamy, heterogamy and egg reproduction. Asexual reproduction produces swimming spores or immobile spores. Zoospores and gametophytes have two unequal lateral flagella, usually long forward and short backward. There are usually generations alternation, generations alternation of the same type and generations alternation of different types.
2. Classify and represent plants
There are about 30 species of Laminaria, which are very common in China. It is people's favorite food. Kelp requires low water temperature, the average temperature in summer is less than 20℃, and the optimum temperature for sporophyte growth is 5- 10℃.
The sporophyte of kelp is divided into three parts: fixator, stalk and belt. The fixer is in the form of branch root; The stem is cylindrical or slightly flat without branches, and the stem tissue is divided into epidermis, cortex and pith. The girdle grows on the stem, is unbranched, has no midrib, and is often skinny when young. Its internal structure is similar to that of stalks, and it is also divided into three layers.
The life history of kelp has obvious generational alternation. When the sporophyte matures, rod-shaped single-chamber swimming sporangia are produced on both sides of the strip, and long cells are sandwiched between the sporangia, which is called lateral fissure. Sporocysts gather into dark brown sporocysts, and the spore mother cells undergo meiosis and many ordinary divisions, producing many homozygous zoospores with unilateral flagella. The zoospores are pear-shaped, with different flagella lengths on both sides (most spores of northern kelp mature in September and June, and a large number of spores are released from the end of June to June). Spores of the same type are physiologically the same and can germinate into male and female gametophytes. Male gametophyte is a branched filamentous body composed of dozens to dozens of cell tissues, and the seminal vesicle on it is formed by a cell, which can produce a sperm with lateral double flagella, and its structure is similar to that of zoospores. The female gametophyte consists of several larger cells with few branches. When there are 2-4 cells, a single-cell oocyst is produced at the end of the branch, which contains a large egg. At maturity, the egg is discharged and attached to the top of the oocyst, and the egg is fertilized outside the mother to form a zygote. The fertilized egg does not leave the mother's body and germinates into a new kelp after a few days. Under suitable conditions, it can grow to 133~ 167cm in June next year. The sporophyte and gametophyte of kelp are very different, and the sporophyte is large and organized. The gametophyte consists of only a dozen cells. So it is the alternation of different generations with developed sporophytes.
Generation alternation: In the life history of some plants, there are two stages of independent life. One is the sporophyte stage, which develops from fertilized eggs and produces spores through meiosis, which is called sporophyte generation; The other stage is haploid gametophyte stage, which develops from spores and produces gametes. Higher plants and more evolved algae have the phenomenon of generation alternation. Algae are widely distributed, and most of them grow in lakes and oceans. They are important links in the food chain of wetland ecosystem and play an important role in maintaining global ecological balance. The requirements for the environment are very high, indicating the role.
Significance to mankind
Raw materials for industry, chemistry, medicine, etc.
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