Animal and Plant Cells: Structure and Function

• A cell is the basic unit of life.
• There are two types of cells: animal and plant.

Cell Structures and Functions

• Cell membrane: Has 2 layers of lipids with a protein layer in between; selects substances entering and leaving.
• Nucleus: Contains genetic material (chromosomes), regulates cellular activities.
• Cytoplasm: Contains water, glucose, minerals, and vitamins; biochemical reactions take place here.
• Ribosome: Small grains in cytoplasm, responsible for protein formation.
• Mitochondrion: Has 2 membranes, inner membrane has folds; site for aerobic respiration.
• Cell wall: Contains cellulose is freely permeable; protects cell against mechanical damage and gives plant a permanent shape.
• Vacuole: Has a concentrated solution of salts and glucose; stores cell sap (vital chemicals).

Specialized Cells Examples

• Specialized cells have a definite shape and perform a specific function.
• Red Blood Cells (Erythrocytes): Are responsible for transporting O2
  • Has a biconcave shape for movement in blood vessels.
  • Spongy cytoplasm helps compress the cell in small vessels.
  • Absence of nucleus increases surface area for O2 transport.
  • Contains hemoglobin to bind and carry O2.
• Muscle cell: Facilitates bone movement (contract / relax).
  • Has long protein fibers in the cytoplasm for shortening the cell.
• Sperm cell: Fuses with ovum to form a zygote.
  • Streamlined head enables movement toward ovum.
  • Has a tail to assist with swimming.
• Ovum: Fuses with sperm to form a zygote.
  • Has a food store for zygote nourishment.
• White Blood Cells (Leucocytes): Includes Phagocytes and Lymphocytes
  • Phagocytes engulf and digest bacteria; are polymorphs and change cytoplasm shape.
  • Lymphocytes produce antibodies that eliminate bacteria; granular cytoplasm with a lobed nucleus.
• Root hair cell: Absorbs water and mineral ions and anchors plants.
  • Many mitochondria generate energy for ion transport.
  • Finger-like projection enables penetration of soil particles.
  • A large sap vacuole ensures water uptake.
• Xylem cells: Transports water and dissolved minerals from roots.
  • Consists of dead hollow tubes devoid of cytoplasm enabling water flow
  • Cylindrical cells attached end-to-end create a xylem vessel.
  • Has walls are lignified (coated with lignin) to withstand water pressure and support the plant against mechanical damage.
• Nerve Cell (Neuron): Transmits nerve impulses.
  • Very long fibers connect distant body parts.
  • Fibers coated with a sheath prevent message loss and distortion.
• Palisade cell: Produces sugar (starch) through photosynthesis.
  • Has lots of chloroplasts with chlorophyll, elongated shape allows tight packing.
  • Found close to the upper epidermis in order to receive more sunlight.
• Guard cells: Regulate the opening and closing of stomata.
  • Crescent shaped and are paired.
  • Can change shape to open/close depending on time of day.

Cell Organization Levels

• Cells are organized into tissues.
• Tissues are groups of similar cells performing a function.
• Organs are groups of tissues working together to perform a function, like how the heart contains nerve, muscle, and epithelial tissue.
• Systems are groups of organs functioning together like the digestive system which comprises; stomach, mouth, intestine, and liver.
• An organism comprises different systems working together like human beings comprises; nervous, skeletal, circulatory, digestive, and muscle systems.

Movement of Substances

• Three processes facilitate substance movement in and out of cells: Diffusion, Osmosis, and Active transport.

Diffusion

• Diffusion is the random movement of particles from high to low concentration until evenly distributed.
• Diffusion occurs in all states of matter.
• In gases: an example of diffusion is perfume spreading in a room.
• In liquids: eg. potassium permanganate spreading in water.
• Diffusion is affected by:
  • Temperature: Increased temperature increases particle kinetic energy, speeding up diffusion.
  • Particle size: Small, less dense particles with large surface areas diffuse faster.
  • Concentration gradient: A large difference in particle concentration speeds up diffusion.

Osmosis

• Osmosis is the movement of water molecules from high to low concentration through a partially permeable membrane.
  • Particles move down the concentration gradient in osmosis.
  • Both processes do not require energy and are passive.

Osmosis and Diffusion

• Osmosis: Occurs mainly in liquids involving the movements of water. Uses a partially permeable membrane.
• Diffusion: Occurs in all states of matter. and Does not require a partially permeable membrane.

Active Transport

• Active transport moves materials from low to high concentration, requiring energy and protein carrier molecules.
• Active transport moves against the concentration gradient, requires energy, and is only used to move mineral ions.

Osmosis and Cells

• A cell can be exposed to pure water/dilute solution or a concentrated solution.

Plant Cell in Pure Water/Dilute Solution:

• Water moves into the cell by osmosis, which increases protoplasm contents.
• This leads to turgor pressure which causes the cell membrane to stretch and touch the cell wall causing the cell to become swollen and turgid.

Plant Cell in Concentrated Solution:

• Water moves out of the cell by osmosis, decreasing protoplasm content.
• This leads to a decrease in turgor pressure as the cell membrane becomes flaccid, pulling away from the cell wall causing the cell to become plasmolysed.

Animal Cell in Pure Water/Dilute Solution:

• Water molecules enter by osmosis, increasing turgor pressure until the cell membrane bursts.

Animal Cell in Concentrated Solution:

• Water molecules exit by osmosis, causing the cell to shrink.

Potato Tissue and Sugar Experiment

• An experiment can be set up to observe the effect of sugar concentration on potato tissue

Apparatus and materials:

• Sugar solutions (0%, 5%, 15%, 25%, 60%).
• Petri dishes
• Cork borer
• White tile and scalpel
• Ruler
• Potato
• Measuring cylinder

Method

• Potato slices are placed in varying sugar concentrations for a period of time
• The change in length for each slice is recorded.
• The data can be used to plot a graph and determine sugar concentration.