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Anonymous users2024-02-13The focus of junior biology is on cells.
There is no uniform definition of cell, and the more common term is that cell is the basic structural and functional unit of living organisms. It is known that all organisms except viruses are composed of cells, but the life activities of viruses must also be reflected in cells.
Generally speaking, most microorganisms such as bacteria and protozoa are composed of a single cell, that is, single-celled organisms, while higher plants and higher animals are multicellular organisms. Cells can be divided into two categories: prokaryotic cells and eukaryotic cells, but some people have proposed that they should be divided into three categories, that is, the ancient karyotic cells that originally belonged to prokaryotic cells should be separated as a parallel category. The discipline that studies cells is called cell biology.
Cells are so small that they can only be seen under a microscope and come in a variety of shapes. It is mainly composed of the nucleus and cytoplasm, and has a cell membrane on the surface. Higher plants have a cell wall outside the cell membrane, plastids in the cytoplasm, chloroplasts and vacuoles in the body, and mitochondria.
Animal cells do not have a cell wall, and centrosomes are often present in the cytoplasm, while higher plant cells do not. Cells have functions such as locomotion, nutrition, and reproduction.
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Anonymous users2024-02-12Top 10 Themes of the Junior High School Biology Curriculum Standards of the People's Education Edition:
1 Science**.
2 Structural hierarchy of living organisms.
3 Biology and the environment.
4 Greenery in the biosphere.
5 People in the biosphere.
6 Movement and behavior of animals.
7 Reproduction, Development, and Heredity of Organisms.
8 Biological diversity.
9 Biotechnology.
10 Live a healthy life.
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Anonymous users2024-02-11There are many points of induction of biology knowledge in junior high school, it depends on what kind of textbook you have? If there is any other publishing house, you had better go to the teacher and ask, the general teacher gives a more complete knowledge induction point, and it is also the focus of the exam.
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Anonymous users2024-02-10Junior high school biology compulsory key knowledge:
(1) The structure and function of the microscope
Stage: A place where a slide specimen is placed. **There are light holes with a tablet clamp on each side to hold the object being observed.
Light shield: There are round holes of different sizes on it, called diaphragms. Each aperture can be aligned with the aperture. It is used to adjust the intensity of the light.
Reflector: It can be rotated to reflect the light through the aperture. The two sides are different: a flat mirror is used for light intensity, and a concave mirror is used for light weakness.
Lens tube: the upper end is equipped with an eyepiece, the lower end is equipped with a converter, and the converter is equipped with an objective lens, and there is a quasifocal spiral at the rear.
Coarse quasi-focal spiral: the amplitude of the lifting of the lens barrel is large when rotating;
Fine Quasifocal Spiral: The amplitude of the lifting of the lens barrel is small when rotating.
The relationship between the direction of rotation and the direction of lifting: turning the quasifocal spiral clockwise, the lens barrel descends; Otherwise, it will rise.
(2) The diagram of the use of the microscope should be mastered
Steps for using the microscope:
Pick up and place the lens: Hold the arm with your right hand and hold the lens holder with your left hand.
Alignment: Turn the converter so that the low-magnification objective is aligned with the clear aperture and a larger aperture is aligned with the clear hole. If you turn the mirror while looking into the eyepiece and see a white bright circular field of view, you will be able to align the light. (Use a wide aperture and concave mirror when the light is low).
Observation: Place the slide specimen to be observed on the stage and press it with a tablet clamp to face the center of the aperture. Turn the coarse collimation spiral so that the barrel is slowly lowered until the objective lens is close to the slide specimen (eyes are looking at the objective lens to the side so that the objective lens does not crush the slide).
One eye looks into the eyepiece, and at the same time rotates the coarse collimation spiral in the counterclockwise direction to make the lens barrel rise slowly, and when the object image is seen, the fine collimation spiral is used to adjust it to make the object image clearer (both the left and right eyes should be opened).
Observation with a microscope Loading The material to be observed with a microscope must be thin and transparent. Therefore, there are three commonly used slide specimens: sectioning, smearing, and mounting.
1) Formed nucleus; (2) cutting off the route of transmission; (3) Specific immunity III; (4) Water, inorganic salts, uric acid, urea and other wastes.
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