Unit 2: Chapter 1 - Cells, Tissues and Organs

Question 1

Animal and Plant Cells

What are the differences between plant and animal cells in terms of their features?

Answer 1

Cells can be seen in more detail using ELECTRON MICROSCOPES.

ANIMAL CELLS (STRUCTURE AND FUNCTION)

• Nucleus: Controls activities of cell. Contains genes in the chromosomes and carry instructions for making new cells or new organisms.
• Cytoplasm: a liquid gel in which most of the chemical reactions needed for life take place.
• Cell membrane: Controls passage of substances into and out of the cell.
• Mitochondria: Structures in the cytoplasm where oxygen is used and most of the energy is released during respiration.
• Ribosomes: This is where PROTEIN SYNTHESIS takes place. All the proteins needed in the cell are made here.

PLANT CELLS (STRUCTURE AND FUNCTION)

Plant cells have the typical features of animal cells but they also have more features:

• Cell Wall: Made out of CELLULOSE that strengthens the cell and gives it support.

Many but not all plant cells have these features:

• Chloroplast: Found in the green parts of the plant. They are green because they contain the substance CHLOROPHYLL. Chlorophyll absorbs light energy to make food by photosynthesis. Root cells do not have chloroplast because they are underground and do not photosynthesise.
• Permanent Vacuole: A space in the cytoplasm filled with cell sap. This is important for keeping cells rigid to support the plant.

Question 2

Bacteria and Yeast

Answer 2

A BACTERIAL COLONY is specific place on the agar jelly where millions of bacteria grow.

BACTERIAL CELL

The Bacteria contains:
- Cell Wall

• Cell membrane
• Cytoplasm
• Genetic material (instead of a nucleus)
• Plasmid: These are circular pieces of DNA that carry extra genetic information.
• Some bacteria may also have a slime capsule around the cell wall.
• Some bacteria have a flagellum or flagella (pl) which is a long protein that lashes about and helps them to move themselves about.

YEAST

The main way yeast reproduce is by ASEXUAL BUDDING. This involves a new yeast cell growing out from the original cell to form a new separate yeast organism.

Yeast or specialise to be able to survive in conditions where there is very little oxygen.

When there is plenty of oxygen they use AEROBIC RESPIRATION which releases CO2 and water as waste products.

When there isn’t as much oxygen, yeast ANAEROBICALLY RESPIRES and produces ETHANOL and CO2. This is called FERMENTATION.

Question 3

Specialised cells

Answer 3

Specialised cells carry out particular jobs. When a cell becomes specialised, its structure is adapted to suit the particular job it does. As a result, specialised cells look very different from the typical plant or animal cell. Examples of these are sperm, nerve and red blood cells.

FAT CELLS

• Small amount of cytoplasm. Large amounts of fat.
• Few mitochondria as it needs very little energy.
• They can expand - a fat cell can end up 1000x it original size as it fills up with fat.

CONE CELLS FROM HUMAN EYE

• The outer segment contains special chemical (a visual pigment). This changes chemically in coloured light. It needs energy to change it back to its original form.
• Middle section is packed with lots of mitochondria and releases energy to reform visual pigment. This lets you see continually in colour.
• The final part of the cone cell is a specialised synapse that connects to the OPTIC NERVE. When coloured light makes your visual pigment change, an impulse is triggered. The impulse crosses the synapse and travels along the optic nerve to your brain.

ROOT HAIR CELLS

• Root hairs increase surface area for more water to move into the cell.
• The root cells contain a permanent vacuole that speeds moment of water by osmosis from the soil across the root hair cell.

SPERM CELLS

• Long tail whips from side to side to help it move towards egg.
• The middle section is full of mitochondria, which provides energy for the tail to work.
• The acrosome stores digestive enzymes for breaking down the outer layers of the egg.
• A large nucleus contains genetic information to be passed on.

Question 4

Diffusion

Answer 4

Diffusion is the net movement of particles from an area of HIGH concentration to an area of LOW concentration. All the particles bumping about makes them move about.

RATES OF DIFFUSION

To increase the rate of diffusion, you need:

• a large CONCENTRATION GRADIENT - Diffusion occurs DOWN a concentration gradient.
• TEMPERATURE as the particles will move quicker.
• Bigger SURFACE AREA means more room for diffusion to take place.

DIFFUSION IN LIVING ORGANISMS

Oxygen is diffused into red blood cells. The oxygen moves down the concentration gradient from high levels to low levels.

Question 5

Tissues and Organs

Answer 5

Similar specialised cells are group together form tissues

TISSUES

A tissue is a group of cells with similar structure and function working together.
e.g. MUSCLE tissue can contract to bring movement. GLANDULAR tissues contain secretory cells that can produce substances such as enzymes and hormones. EPITHELIAL tissue covers the outside of your body as well as internal organs.

Plants also have tissue such as EPIDERMAL tissues covers the surface and protects them. MESOPHYLL tissues that contains lots of chloroplast and carry out photosynthesis. XYLEM and PHLOEM are the transport tissues in plants.

ORGANS

Organs are made out of tissues. On organ can contain several tissues. For example, the stomach contains muscular, glandular and epithelial tissue.

The organs are groups of tissues that carry out important functions.

Different organs combined in ORGAN SYSTEMS carry out major functions in the body such as transporting blood or digesting food. These organ systems make up your body.

Question 6

Organ Systems

Answer 6

THE DIGESTIVE SYSTEM

You ingest INSOLUBLE molecules. They need to broken down in order to digest these smaller, soluble molecules. This process of digestion takes place in the DIGESTIVE SYSTEM.

Starting from the mouth, there are SALIVARY GLANDS that secrete digestive enzymes. The enzymes in your salivary glands produce carbohydrases. An example of this would be AMYLASE.

You food then moves through the oesophagus down to the stomach and the small intestines where food is digested. From the small intestine, food is absorbed into the villi.

PLANT WALLS

Plants have organs too.

The mesophyll layer carries out photosynthesis and then absorbed by the xylem and the phloem.

The XYLEM transports WATER and MINERALS.

The PHLOEM transports DISSOLVED FOOD.

Question 7

Photosynthesis

Answer 7

Photosynthesis equation:
CO2 + WATER -> OXYGEN + GLUCOSE

The cells in algae chloroplast. Within these chloroplasts are chlorophyll which carries out photosynthesis.

Some of the glucose produced by the plants are immediately absorbed.
However a lot of the glucose in converted to insoluble starch to STORE.

LEAF ADAPTATIONS

• Most leaves are broad, giving them a large surface area for light to fall on.
• They contain chlorophyll in chloroplast to absorb light energy.
• They have air spaces that allow CO2 to get into the cells of the leaves.
• They have veins which quickly transports plenty of water to cells of the leaves.

These adaptations allows plants to photosynthesise at their optimum level.

Algae are aquatic and are adapted to photosynthesise in water. They absorb CO2 dissolved in water.