Ch 10: Cells to Multicellular Organisms

Question 1

How are cells organised, how are they classifyed and what similar overal pattern do they share?

Answer 1

Cells are organised in a hierarchy of structural levels.

There are patterns in the basic structural organisation of cells.

These patterns are used to classify cells as either

• prokaryotic or
• eukaryotic.

All share a similar overall pattern:

• plasma membrane
• cytosol
• genetic material
• ribosomes.

Question 2

What are features of unicellular organisms?

Answer 2

• key limitation is related to the number of metabolic activities that can be performed within the cell at one time.
• complete functioning organisms. All the needs of the organism (e.g. nutrients, energy and water) and functions (e.g. intake of nutrients and energy, processing of nutrients to release energy, and expulsion of waste products) take place within the boundary of the cell.
• The microscopic size of the cell allows these processes to occur efficiently.
• A single cell has a high surface area to volume ratio. This means that the size of the plasma membrane (its surface area) is sufficient to service the total volume of the cytoplasm. Oxygen, nutrients and carbon dioxide can diffuse directly across the plasma membrane in amounts sufficient to meet the needs of the entire cell.

colony - an orgnaised association of unicellular organisms

Question 3

How did the evolution from unicellular organisms to multicellular organisms occur?

Answer 3

The evolution from unicellular organisms to multicellular organisms required three organising principles.

1. Cell division
2. Specialisation (one function)
3. Communication with other cells

Question 4

What is differentiation?

Answer 4

process in which cells become more specialised as they mature

Question 5

What are stem cells and how are they different to normal cells?

Answer 5

• unspecialised cells and immature
• all specialised cells originate from stem cells
• Stem cells differ from other cells in the body in three important ways.
  
  1. that they are unspecialised (have not yet specialised into a particular type of cell).
  2. they have the potential to divide and replicate for long periods of time.
  3. can differentiate to form different specialised cells.

Question 6

What are benefits and costs of specialised cells?

Answer 6

specialised cells - cells that posses specific features suited to its function

benefits

• increase efficiency
• reduce duplication of effort
• essential for survival

costs

• reliant on communication and coordination between cells (activities of other cells), if a specialised cell was isolated from the organism it is part of, it will not be able to function on its own and die

Question 7

How do mutlicellular organsisms have identical cells yet with different functions?

Answer 7

• The genetic info in cells of multicellular organisms is identical
• They are able to perform and look differently as only a small portion of the genetic info is ‘switched on’
• As cell layers migrate in the embryo to different regions, genes are switched on or off in response to neighbouring cells and environmental cues.
• Cell appearance and function is determined by active genes.
  *

Question 8

What are the four main tissues?

Answer 8

Cells form tissues

• Multicellular organism have four major tissue divisions:
  
  • epithelium
  • connective tissue
  • nervous
  • muscle.

Question 9

What is the multicellular organism organisation?

Answer 9

In multicellular organisms cells of similar shape and function are organised into tissues. Different tissues are organised into an organ that carries out a particular function.

Groups of organs working together to achieve a particular function make up a system.

Question 10

What is connective tissue?

Answer 10

provides support and holds parts of the body together. Plays a key role in binding and supporting other tissues and protects against damage, infection and heat loss

• cells are sparsely scattered through a semi-fluid extracellular matrix
• main types:
  
  • loose connective
  • firbous connective
  • adipose tissue
  • cartilage
  • bone
  • blood
• i.e. human red blood cells are small, enabling them to move easily through capillaries. Loss of their nucleus as they mature gives these cells more space to carry oxygen

Question 11

What is epithelial tissue?

Answer 11

covering that protects organs, lines body cavities and covers the surface of the body (protects internal and external surfaces)

• epithelial cells are usually organised into tightly packed single or layered sheets. This cell organisation increases their effectiveness as barriers which protect against mechanical injury, invasive micro-organisms and loss of fluid.
• some epithelial tissue may be specialised to function in absorption, secretion or excretion.
• i.e.the epithelium tissue that lines the respiratory tract secretes mucus that lubricates the surface and keeps it moist. The possession of cilia enables the mucus to move along the surface, trapping particles and sweeping them back up the trachea. This helps to keep lungs clean and healthy.

Question 12

What is muscle tissue?

Answer 12

made up of thin and very long thread-like cells called muscle fibres. These fibres are capable of contracting when stimulated by nerve impulses.

• Contraction of these fibres accounts for much of the energy requirements in an active animal.

Question 13

What is nervous tissue?

Answer 13

provides the means of communications between all body structures and its cells are highly specialised

• i.e. motor neurons - elongated shape and extensions well suited to its function of passing messages between the nervous system to other parts of the body
• the shape of the dendrites increases the SA for message detection. The electrical message (impulse) is then carried along the axon to the axon terminal where it is converted into a chemical message (neurotransmitter) which is then released into the synapse. The message may either interact with another neuron or an affector (i.e. muscle or gland) to bring about a response

Question 14

How are the organs grouped in a vascular plant?

Answer 14

The structure of a vascular plant ensures that each organ, the leaves, stem, roots, flowers and seeds, receives what it needs. The organs are grouped as systems and in plants there are two systems.

1. The shoot system is comprised of all parts of the plant found above ground. This includes the plant stem as well as the leaves and reproductive organs which grow from the tips of actively growing stems. The shoot system is responsible for supporting the plant physically and the transportation of resources, as well as the absorption of oxygen and carbon dioxide, reproduction and carrying out photosynthesis in leaves.
2. The root system is generally below ground and is responsible for absorbing water and nutrients from the soil. The roots and root hairs are part of the root system.

Question 15

What are the 4 main types of tissue in plants?

Answer 15

Vascular plants have four main types of plant tissues. These tissues perform specialised functions such as storage, transportation, photosynthesis and growth.

• Meristematic tissue is composed of cells that undergo cell division by mitosis, the process by which plants grow. Meristems are the only places in a plant where cells divide; they are located: at the tips of roots and shoots and in a ring around the inside of stems and branches. This enables growth in length as well as width. Some meristematic cells differentiate after division.
• Dermal tissue is composed of the outermost cell layers of a plant. It protects the cells from cuts, invasion by micro-organism and water loss. The epidermis is the outermost part of the dermal layer. On leaves and stems, these cells usually produce a waxy cuticle. This wax is vital to the prevention of water loss from leaves and other delicate tissues. Epidermal cells also produce fine hairs on the surfaces of many leaves and stems. In many plants, these discourage plant eaters. Some contain harmful irritants that are released into the skin when touched. Epidermal root tissue produces large numbers of extremely fine extensions called root hairs. These hairs aid in the absorption of water and minerals. In woody plants, bark layer forms when layers of dead specialised cells replace the epidermis.
• Ground tissue is composed of all the internal cells of a plant other than vascular tissue. This tissue consists of a variety of different cell types that are specialised for storage, support and photosynthesis.
• Vascular tissue: involved in the transport of substances