Cells and homeostasis

Question 1

What are the 3 basic principles of cell theory?

Answer 1

-All living organisms are composed of one or more cells.
-A cell is the basic structural and functional unit of living organisms.
-All cells arise from pre-existing cells.

Question 2

Cell structure

Answer 2

cytoplasm
cytosol
organelles (mitochondria, smooth endoplasmic reticulum (SER), rough endoplasmic reticulum (RER), Golgi apparatus, lysosomes, cytoskeleton, centrioles, ribosomes)

Question 3

Nucleus

Answer 3

All body cells have at least 1 nucleus.
Largest organelle and contained within nuclear envelope.
Contains body’s genetic material
Also contains the nucleolus, involved in synthesis of some ribosomes

Question 4

Endoplasmic reticulum

Answer 4

Extensive series of interconnecting membranous canals. Two types, smooth and rough

Smooth - synthesises lipids, steroid hormones and vesicles to transport them to other parts of the cell

Rough - studded with ribosomes, site of protein synthesis. Enzymes and hormones are exported out the cell by exocytosis for use elsewhere

Question 5

Vesicle

Answer 5

A structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer’ used for transportation

Question 6

Ribosomes

Answer 6

Granules of RNA and protein.
Uses the RNA to synthesise proteins from amino acids for use in the cell.
Found on outer surface of nuclear envelope and RER.

Question 7

Mitochondria

Answer 7

Powerhouse of the cell.
Central to aerobic respiration, making chemical energy in the form of ATP.
Released energy when cell breaks down ATP.
This process requires oxygen.
Most active cell types have greatest number of mitochondria.

Question 8

Golgi apparatus

Answer 8

Stacks of folded flattened membranous sacs with vesicles budding from it.
Proteins move from RER to golgi where packaged into membrane bound vesicles. These are stored for when needed.

Question 9

lysosomes

Answer 9

Small vesicles pinched off from the golgi.
Membrane bound.
Contain enzymes and large molecules like DNA, carbohydrates, proteins.

Question 10

Cytoskeleton

Answer 10

Extensive network of tiny protein fibres.

Provides internal support for the cell, Anchors organelles as well as guiding movement around cell interior.

Question 11

Microfilaments

Answer 11

protein fibres anchored to inside of cell membrane, giving support and shape

Question 12

Microtubules

Answer 12

large rigid proteins giving mechanical support, providing guidance tracking for internal movement.

Question 13

Centrosome

Answer 13

directs organisation of microtubules within the cell. Consists of pair of centrioles.

Question 14

Plasma membrane

Answer 14

Selective barrier, controls passage of substances in and out of the cell, regulating intracellular environment.

Question 15

How many layers of phospholipids are there?

Answer 15

Two layers of phospholipids with proteins, cholesterol and glucolipids imbedded.

Question 16

What are phospholipids?

Answer 16

Phospholipids have a hydrophilic head and hydrophobic tail. Heads on outer surfaces, tails sandwiched in between. Affects how substances are transported across the membrane.

Particle size affects how transported across membrane, if at all.

Question 17

What are the 2 kinds of transport?

Answer 17

passive and active.

Question 18

Diffusion + facilitated diffusion

Answer 18

The movement of molecules from an area of high concentration to an area of low concentration.

Factors can affect the rate, including temperature or concentration.
Molecules need to be small or soluble enough to cross membrane with diffusion alone.

Lipid soluble materials cross the lipid part of the membrane. Water soluble cross through water-filled channels.

Facilitated diffusion- some substances unable to diffuse across membrane, e.g. glucose, amino acids. need protein carrier molecules to aid diffusion.

Question 19

Osmosis

Answer 19

osmosis refers specifically to diffusion down a concentration gradient.
Usually because other molecules are too large to pass through membrane
Force at which this occurs is called osmotic pressure.
Movement is to achieve equilibrium in concentration not necessarily volume, this is called isotonic

Question 20

Active transport

Answer 20

Transporting substances up the concentration gradient from lower concentration gradient to higher concentration gradient.
To do this requires energy in the form of ATP

Sodium potassium pump - supports transport mechanisms such as glucose uptake.

Also is essential in maintaining the electrical gradient needed to generate action potentials in nerve and muscle cells.

Active transport maintains the unequal concentrations of sodium and potassium ions either side of plasma membrane.

Question 21

Cell cycle

Answer 21

An ordered sequence of events including duplication of cellular contents and division that all cells follow.

For growth and repair.

The rate of replication varies with different types of tissues.

Aged cells ‘self destruct’ known as apoptosis.

Question 22

Cell cycle: What are the 4 discrete phases?

Answer 22

G1 - gap phase - cells grow in size, some do not prepare for division but instead, ‘rest’ (G0)- specific cellular functions. Cells may stay in G0 for whole life span.

S - synthesis phase, DNA replication, 2 identical copies. Cell now has 92 chromosomes

G2 – gap phase, further growth and preparation for division

M – mitosis phase, cell divides

Question 23

What are the 2 types of cell division?

Answer 23

Mitosis and meiosis

Question 24

Explain mitosis

Answer 24

-Occurs in somatic (non-reproductive) cells for growth and repair
-One round of replication
-One division
-1 parent cell produces two identical daughter cells (2n)
-No genetic diversity
-cell contains 46 chromosomes

Question 25

Explain meiosis

Answer 25

-Occurs in reproductive cells- formation of gametes (egg and sperm)
-Not a ‘cell cycle’, linear because of its products
-One round of DNA replication
-Two successive divisions
-Results in four different daughter
cells that contain half the number of chromosomes of the parent cell (1n)
- Each daughter cell contains 23 chromosomes, haploid cells

Question 26

5 stages of mitosis

Answer 26

Prophase - Chromosomes appear condensed, nuclear envelope no longer apparent. Centrioles begin moving to opposite ends of the cell and fibres extend from the centromeres.

Metaphase - Spindle fibres align the thick, coiled chromosomes, each made of 2 chromatids, along the middle of the cell nucleus; referred to as the metaphase plate.

Anaphase - The paired sister chromatids separate and move to opposite sides of the poles of the cell as the spindles shorten.

Telophase - Chromatids arrive at opposite poles of cell, and new nuclear membranes form around the daughter nuclei. Chromosomes become more diffuse. Spindle fibres disperse, cytoplasm may begin dividing.

Cytokinesis - Cell division is complete and two identical daughter cells are produced. Chromosomes start to decondense, and the cells return to interphase.

Question 27

Meiosis- Genetic recombination

Answer 27

Genetic recombination happens in meiosis. Where two molecules of DNA exchange parts of genetic material when homologous chromosomes are lined up in pairs.

This is known as chromosomal crossover or “crossing over”

Results in new genetic combinations – creates genetic variation/diversity

Due to genetic recombination, any offspring will have a different combination of alleles and genes than their parents do

Question 28

Homeostasis

Answer 28

Keeping a stable constant internal environment via use of negative feedback e.g. regulating temperature and chemical levels.

The homeostatic process ensures that variables never deviate outside of the normal perimeter

Afferent pathway- to the control center

Efferent pathway- to the effectors
Stimulus detected- deviation from set point

Receptors detect these changes
Control centre generates a response to make changes
Effectors carry out that response

Question 29

Homeostasis: What are the 2 types of bodily fluid

Answer 29

Intracellular fluid- within cells

Extracellular fluid- outside cells

Content of both fluids is: water, oxygen, nutrients, proteins and various ions

Question 30

Homeostasis: Types of extracellular fluid

Answer 30

Interstitial fluid- around cells and tissues
Plasma- within the blood
Lymph- within lymphatic vessels
Cerebrospinal fluid- around and in the brain and spinal cord
Synovial fluid- within joints

Question 31

What happens to the composition of fluid during homeostasis?

Answer 31

Composition of fluid changes as it moves between it and blood plasma due to various forces; hydrostatic pressure (force pushing fluid out of vessels occurs in arteries due to heart pumping) and osmatic pressure (due to concentration differences, passing from high concentration to low concentration tends to occur at venous ends).

This process allows the movement of materials into the interstitial required by cells and the removal of waste products e.g. carbon dioxide.

Homeostatic imbalances can result in disorder and disease.

Question 32

What are feedback systems and what are the 2 types?

Answer 32

Generally the nervous and endocrine system tend to be responsible for maintaining homeostasis. These systems can work independently or together.

The nervous system sends nervous impulses.
The endocrine results in the release of hormones into the blood.

Two types of feedback system:
-Negative feedback
-Positive feedback - amplification of symptoms.
Examples of positive feedback include contractions/labour and breastfeeding

Question 33

Feedback systems: What affects the body’s control system?

Answer 33

Age affects the body’s control system becoming less efficient resulting in a less stable internal environment.

Occasionally the negative feedback system can become overwhelming and the positive feedback system results leading to potentially life-threatening situation (heart failure).