Biology Summary Chapter 2:
Three states of matter:
Every substance can exist in three states: gas, liquid and solid.
Water can be a solid (ice), a liquid (just water) and a gas (steam)
In a solid the molecules can only vibrate – they can’t move out of position.
They’re held together by strong forces between the molecules.
This gives a solid a definite shape.
In a liquid the molecules are moving slowly.
Forces between the molecules hold them together more closely than in a gas.
In a gas the molecules are moving very quickly.
Dissolving:
- How does it happen that many subsances dissolve in water?
There are tiny spaces between the water molecules.
When something like sugar dissolves, each grain breaks up into thousands of tiny sugar particles. These tiny particles spread out and fit into the spaces between the water molecules.
- A solution is made up of two parts, the solute and the solvent. The solute dissolves in the solvent.A concentrated solution has a lot of solute dissolved in the solvent. A dilute solution has a small amount of solute dissolved in the solvent.
Diffusion:
Diffusion is the movement of particles from a high concentration to a low concentration until they spread out evenly.
Osmosis:
Osmosis is the passage of water meolecules from a weaker solution into a stronger solution through a partially (also called semi) permeable membrane.
Water will move into plant cells by osmosis.
1. The cell membrane of the plant cell acts as a partially permeable membrane.
2. The cell sap inside the vacuole is a strong solution.
3. Water passes into the plant cell by osmosis.
4. The concentration of the sap in the vacuole is now weaker.
5. Water passes from the weak solution into the strong solution in the next cell by osmosis.
Turgidity:
When plant cells are placed in water, the water enters the cells. This is because their cell sap contains a strong solution. So water passes into the cells by osmosis. The cell membrane is a partially permeable membrane.
As water enters it makes the cell swell up. The water pushes against the cell wall. Evantually the cell contains as much water as it can hold. It’s like a blow-up balloon. The strong cell walls stopt the cell bursting. We say that the cell is turgid.
Turgid cells give the plant support. They keep the stems of many plants upright.
When the cell loose water, the cells aren’t longer firm and turgid. Plants stems that have lost water wilt.
Plasmolysis:
Now, what happens if you put a plant cell into a solution which is stronger than that in the vacuole? In this case water is drawn out of the vacuole and the cell shrinks: it loses its turgor and becomes flabby or flaccid. Ift he external solution is strong enough, the vacuole and cell membrane eventually pulls away from the cell wall. We call this process plasmolysis.
Summary of the summary:
- Everything is made up of molecules that are always moving.
- Molecules move from a high concentration to a low concentration by diffusion.
- Food and oxygen diffuse into cells.
- Carbon dioxide and wast substances diffuse out.
- Osmosis is the movenment of water molecules from a weak solution into a strong solution through a partially permeable membrane.
- Water passes into plant cells by osmosis. A plant cell that is full of water is turgid. If plant cells are places in a strong solution, water passes out by osmosis. As the vacuole shrinks the cell membrane eventually peels away form the cell wall – the cell is plamolysed.
- If animal cells are put into a weak solution they take in water and burst.
Three states of matter:
Every substance can exist in three states: gas, liquid and solid.
Water can be a solid (ice), a liquid (just water) and a gas (steam)
In a solid the molecules can only vibrate – they can’t move out of position.
They’re held together by strong forces between the molecules.
This gives a solid a definite shape.
In a liquid the molecules are moving slowly.
Forces between the molecules hold them together more closely than in a gas.
Dissolving:
- How does it happen that many subsances dissolve in water?
There are tiny spaces between the water molecules.
When something like sugar dissolves, each grain breaks up into thousands of tiny sugar particles. These tiny particles spread out and fit into the spaces between the water molecules.
- A solution is made up of two parts, the solute and the solvent. The solute dissolves in the solvent.A concentrated solution has a lot of solute dissolved in the solvent. A dilute solution has a small amount of solute dissolved in the solvent.
Diffusion:
Osmosis:
Osmosis is the passage of water meolecules from a weaker solution into a stronger solution through a partially (also called semi) permeable membrane.
Water will move into plant cells by osmosis.
1. The cell membrane of the plant cell acts as a partially permeable membrane.
2. The cell sap inside the vacuole is a strong solution.
3. Water passes into the plant cell by osmosis.
4. The concentration of the sap in the vacuole is now weaker.
5. Water passes from the weak solution into the strong solution in the next cell by osmosis.
Turgidity:
When plant cells are placed in water, the water enters the cells. This is because their cell sap contains a strong solution. So water passes into the cells by osmosis. The cell membrane is a partially permeable membrane.
Turgid cells give the plant support. They keep the stems of many plants upright.
When the cell loose water, the cells aren’t longer firm and turgid. Plants stems that have lost water wilt.
Plasmolysis:
Now, what happens if you put a plant cell into a solution which is stronger than that in the vacuole? In this case water is drawn out of the vacuole and the cell shrinks: it loses its turgor and becomes flabby or flaccid. Ift he external solution is strong enough, the vacuole and cell membrane eventually pulls away from the cell wall. We call this process plasmolysis.
Summary of the summary:
- Everything is made up of molecules that are always moving.
- Molecules move from a high concentration to a low concentration by diffusion.
- Food and oxygen diffuse into cells.
- Carbon dioxide and wast substances diffuse out.
- Osmosis is the movenment of water molecules from a weak solution into a strong solution through a partially permeable membrane.
- Water passes into plant cells by osmosis. A plant cell that is full of water is turgid. If plant cells are places in a strong solution, water passes out by osmosis. As the vacuole shrinks the cell membrane eventually peels away form the cell wall – the cell is plamolysed.
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