Unit 2 Movement of materials in and out of cells

1. Describe the process of diffusion as the result of the random movement of particles in liquids and gases down a concentration gradient

2. Describe the factors that affect the speed of diffusion.

3. Be aware that diffusion can effectively transport substances only over short distances within living organisms. 

4. Give a simple description of cell membrane structure and describe how this structure determines the permeability of the membrane to different substances. (Vocab: permeable, impermeable, protein, fat [lipid] soluble, water-soluble.)

5. Explain the following mechanisms by which materials enter or leave the cell: simple diffusion, facilitated diffusion, active transport, exocytosis and endocytosis [pinocytosis and phagocytosis]. (Vocab: protein carrier, active process, passive process, vesicle.) Give examples of the type of substances transported by each mechanism. 

6. Define osmosis

7. Explain the consequences of placing animal and plant cells and tissues in hypotonic, isotonic, and hypertonic solutions. (Vocab: turgid, flaccid, plasmolysis/plasmolysed.) Discuss the importance of osmosis for animals and plants.

8. Explain the role of the contractile vacuole in freshwater protozoa such as Paramecium.

Lo. 1 Describe the process of diffusion as the result of the random movement of particles in liquids and gases down a concentration gradient.

What is diffusion?

It is the process of movement of particles from an area of high concentration to a low concentration. it happens in liquids and gases since their particles move randomly.

What causes diffusion?

Since gases and liquids move randomly, it means they have kinetic energy. The particles collide with each other randomly, causing changes in direction eventually, the particles become spread out. Diffusion happens on its own.

What is a gradient?

A gradient is an increase or decrease along a scale. Examples temperature, color, pressure

What is a concentration gradient?

It means the difference in concentration between 2 regions.

A high concentration gradient means that there’s a large difference where molecules are spread out, causing them to move faster from a crowded area to the empty space that is spread.

A low concentration means there only a small difference in how many molecules are in one area compared to another.

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Diffusion occurs because particles are moving and the concentration gradient exists. Diffusion will stop once there is no concentration gradient and particles have equal concentration in all areas. When all particles are evened out is called equilibrium.

Even when the diffusion is stopped at equilibrium the particles are still in constant motion.

Lo.2

Describe the factors that affect the speed of diffusion.

concentration

mass

temperature

Lo.3 Be aware that diffusion can effectively transport substances only over short distance within living organisms.

Diffusion in living organisms is made up of water, which makes diffusion slightly slow.

Characteristics of diffusion

• Diffusion is fast enough to transport substances within cells

• Diffusion is fast to transport substances over short distances between cells

• It isnt fast to transport substances between different parts of a large organism.

Diffusion in the body:

Gas exchange. Gases diffuse from a higher concentration to lower concentration occurring in the lung's air sacs.

Lo. 4

Give a simple description of cell membrane structure and describe how this structure determines the permeability of the membrane to different substances.

Define: dissolved :

salt(solute) can be dissolved in water(solvent) to make salt water(solution)

Dissolved is when a substance breaks down into smaller pieces, it doesn’t mean it melted.

Cell membrane

• Holds cells together and leads materials in and out

• Allow dissolved substances to move in and out by diffusion

• Only small molecules diffuse through the cell

• Don’t allow big molecules, such as proteins, to diffuse through the membrane

• Have two layers of phospholipids, which are fluid and very flexible

• Have many proteins on their surface

• These proteins serve various functions, including transport, signaling, and providing structural support, contributing to the overall functionality of the cell membrane.

Question.

Is mixing the same as diffusion?

-→ Yes, as they both help to spread out substances evenly.

Permeability of the cell membrane

Meaning of permeability → Allows substances to pass through

Cell membranes are selectively permeable, meaning that they regulate which substances can be let in and which cannot.

Water, oxygen, and carbon dioxide can pass directly through the phospholipids in the cell membrane. Whereas larger molecules, such as glucose, require a specific protein to help transport their movement.

Lo 5 Explain the following mechanisms by which materials enter or leave the cell:

simple diffusion, facilitated diffusion, active transport, exocytosis, and endocytosis. (phagocytosis and phagocytosis)

Give examples of the type of substance transported by each mechanism.

1. Simple Diffusion

-→ Substances diffuse through the cell membrane straight through the phospholipids. They are usually small or fat-soluble substances. (o2, Co2, fatty acids)

The diffusion occurs down the concentration gradient from high to low and occurs without any energy input required.

2. Facilitated Diffusion

→ Involves diffusion facilitated by transport Proteins

Each protein transports a specific substance. They are either medium-sized or water soluble(glucose, amino acids, water, ions)

This diffusion occurs down the concentration gradient and does not require energy.

3. Active Transport

→ energy is required since the substances are moving up the concentration gradient, from low concentration to high concentration

But they transport the same substances as facilitated diffusion

4. Bulk transport

→ Protein molecules are too big to pass through the cell membrane, but can pass through by being enclosed in a vesicle a small sac of the membrane. This process requires much energy and is an active process.

Endocytosis

→ Transports large substances into the cell

(phagocytosis) is sometimes called cell eating as Amoeba eats paramecium and white blood cell eats bacteria,

The membrane engulfs the substance to form a vesicle

Pinocytosis is sometimes called cell drinking

Exocytosis

→ Transports large substances out of the cell

eg, Paramecium excretes waste, and salivary glands secrete the enzyme amylase into saliva

Lo6.

Define Osmosis

what is Osmosis

→ It is the diffusion of water

More specifically osmosis is the net movement of water molecuels across a selectively permeable membrane from a place of low solute concentration to an area of high solute concentration. It continues until reaching equilibrium on both sides of the mebrane.

Solute is the substance dissolved in a solution

Lo7

Explain the consequences of pacing animal and plant cells and tissues in hypotonic, isotonic, and hypertonic solutions. (vocab: turgid, flaccid, plasmolysis)

Discuss the importance of osmosis for animals and plants.

Osmosis has 3 different types of solutions, which are

Isotonic, Hypotonic, and Hypertonic

Isotonic means that it has the same concentration of solutes and solvent

Hypertonic means more solutes and fewer solvents (more dissolving substances)

Hypotonic means fewer solutes and more solvents. (more water)

Osmosis in animal cells

If red blood cells were placed in the same water solution as their cytoplasm, there would be no overall change, as the cells are isotonic to the solution. Meaning no osmosis occurs.

Blood cells surrounded in a hypotonic solution will swell and burst. This is due to the fact that they are being placed in a solution with a higher water concentration than their content. The water will diffuse from a high water concentration to a low water concentration inside the cell.

Blood cells put into a Hypertonic solution will shrivel as they are being put into a solution with a lower concentration than their contents; they will lose water by osmosis. Which causes them to shrivel. The water will diffuse from a high water concentration inside the cell to a low water concentration outside the cell.

Explain what happened to the onion cells.

The onion cells on the right are in a hypertonic solution (an environment that has less water). Due to this, most water leaves the cells through osmosis, causing the cell membrane to pull away from the cell wall, leading to shrinkage.

Osmosis in Plant Cells

A healthy plant with lots of water supply is in a hypotonic environment. They gain water through osmosis by pushing against the cell walls, making it to be firm and hard (turgid)

If the plant is placed in hypertonic surroundings it can occur natural when in shortage of water ,the plant will lose water by osmosis. As the cells shrink, the cell membrane will no longer push on the cell wall, causing it to become flaccid. When it becomes flaccid, the plant will wilt as the leaves soften and stems droop. The cell membrane has shrunk away from the wall and is said to be plasmolysed.

Advice on writing clearly about osmosis in living cells.

1. Are the cells in hypotonic, hypertonic, or isotonic surroundings?

2. Is there a net water movement in or out of the cells by osmosis, or overall no water movement?

3. What is the effect on the cells of any water movement that happens? For plant cells, describe whether they are turgid or flaccid.

Lo 8 explain the role of the contractile vacuole in freshwater protozoa as Paramercium

A paramecium → a unicellular eukaryote, they are found in aquatic habitats and are usually covered with short, hairy structures called cilia.

Paramecium does not have a cell wall, so in a hypertonic or hypotonic solution, it could burst or shrivel.

Normally, the concentration of solutes inside the paramecium is higher than outside the cell so it lives in a hypotonic enviroment. In order to stop itself from bursting it expels water using the contractile vacuoles. Which collect excess water from the cytoplasm and releases it outisde th cell.