Chapter 2: Cells

Question 1

Outline the cell theory

Answer 1

• Living organsim are composed of cells
• Cells are the smallest nuits of life
• Cells come from pre-existing cells

Question 2

Which functions of life carry unicellular organism out?

Answer 2

Metabolism
Homeostasis
growth
reproduction
nutrition

Question 3

Compare the relative size (increasing order)

Answer 3

Animal/plant cell
organelles
bacteria
virus
cell membranes
Molecules (e.g. DNA)

Question 4

Calculate magnification

Answer 4

size of the picture/actual size of the object

Question 5

Explain the importance of the surface area to volume ratio as a factor limitating cell size

Answer 5

enter/leave - surface area
used/produced - volume
If a cell is to large then the volume is to big and the surface area is to small. This makes it hard for the cell to move materials in and out

Question 6

Multicellular organism show emergent propérties

Answer 6

Emergent properties arise from the interaction of component parts: the whole is greater than the sum of its parts

Question 7

Explain that the cells in multicellular organism differentiate to carry out specialized functions by expressing one of their genes but not others

Answer 7

• Cells in a multicellular organism develop in different ways and can therefore carry out different functions. This is called differentiation.
• The cell needs different genes to develop in different ways.
• Each cell has all of these genes, so could develop in any way.
• The cells will express some of their genes but no other.

Question 8

Outline one therapeutic use of stem cells

Answer 8

The placenta and umbilical cord of a baby is used as a source of stem cells. At the end of childbirth, the placenta is taken and placed on a strand, with the umbilical cord hanging down from it. Blood drains out of the umbilical cord and is collected. The cord blood contains many hematopoietic stem cells. These cells can divide and differentiate into any type of blood cell.

Question 9

Cell wall

Answer 9

forms a protective outer layer that prevents damage from outside and also bursting of internal pressure is high

Question 10

Plasma membrane

Answer 10

controls entry and exit of substances, pumping some of them in by active transport

Question 11

Cytoplasm

Answer 11

contains enzymes that catalyse the chemical reactions of metabolism and contains DNA in a region called nucleoid

Question 12

Pili

Answer 12

hair-like structures projecting from the cell wall, that can be ratcheted in and out; when connected to another bacteria cell they can be used to pull cells together, adhesion.

Question 13

Flagella

Answer 13

using energy they can be rotated to propel the cell from one area to another

Question 14

Ribosomes

Answer 14

Small granular structures that synthesise proteins by translating messenger RNA. Some proteins stay in the cell and others are secreted

Question 15

Nucleoid (region containing naked DNA)

Answer 15

Region of the cytoplasm that contains naked DNA, which is the genetic information in the cell

Question 16

How do prokaryotes divide?

Answer 16

prokaryotic cells divide by binary fusion

Question 17

Lysosome

Answer 17

bound by a single membrane. They contain and transport enzymes. They are formed from Golgi vesicles. Contain high concentrations of proteins. Use enzymes to break down ingested food or organelles in the cell

Question 18

Golgi apparatus

Answer 18

stores, modifies and packages proteins

Question 19

Mitochondrion

Answer 19

Organelles that carry out respiration. They produce ATP for the cell by aerobic cell respiration

Question 20

Prokaryotic cells

Answer 20

Bacteria and Archea

• No membrane bound organelles = no organelles with membranes
• No nucleus = no membrane around the DNA
• Naked DNA = no proteins attached to the DNA

Question 21

Eukaryotic cells

Answer 21

Plant cell, Animal cell, Fungi and Protists

• Have a nucleus
• Have proteins attached to the DNA
• Have membrane bound to organelles

Question 22

State 3 differences between a plant and animal cell

Answer 22

• Plant cells have chloroplast
• Plants cells have a fixed shape, whereas animal cells are able to change shape
• Plants cells have a cell wall

Question 23

Outline 2 roles of extracellular compounds

Answer 23

• The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the whole plant up against the force of gravitation.
• Animal cells secrete glycoproteins that from the extracellular matrix. This functions in supporting adhesion and movement.

Question 24

Integral proteins and peripheral proteins

Answer 24

Integral proteins are embedded in the phospholipid of the membrane, whereas peripheral proteins are attached to its surface.

Question 25

Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of the cell membranes

Answer 25

• Hydrophilic molecules are attracted to water.
• Hydrophobic molecules repel water, but are attracted to each other.
• The phosphate head is hydrophilic and the two hydrocarbon tails are hydrophobic.
• In water, phospholipids form double layers with the hydrophilic heads in contact with water on both sides and the hydrophobic tails away from the water centre.
• This arrangement is found in biological membranes. The attraction between the hydrophilic heads and the surrounding water makes membranes very stable.
• This model of the plasma membrane is called THE FLUID MOSAIC MODEL.

Question 26

List the functions of membrane proteins

Answer 26

	Hormone binding sites
	Immobilized enzymes
	Cell adhesion
	Cell-to-cell communication
	Channels for passive transport
	Pumps for active transport

Question 27

Diffusion

Answer 27

the passive movement of particles from a region of high concentration to a region of low concentration.

Question 28

Osmosis

Answer 28

the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.

Question 29

facilitate diffusion

Answer 29

• substances which are unable to diffuse through the membrane
• need protein channels

Question 30

simple diffusion

Answer 30

• Membranes allows some substances to diffuse through but not others – they are partially permeable.
• Some of these substances move between the phospholipid molecules in the membrane

Question 31

What kind of ribosomes have prokaryotes?

Answer 31

70S Ribosomes

Question 32

What kind of ribosomes have eukaryotes?

Answer 32

80S Ribosomes

Question 33

Explain the role of protein pumps and ATP in active transport across membranes

Answer 33

• Active transport is the movement of substances across membranes using energy from ATP.
• Active transport can move substances against the concentration grade – from a region of lower concentration to a region of higher concentration.
• Protein pumps in the membrane are used for active transport.
• Each pump only transports particular substances, so cells can control what is absorbed and what is expelled.
• Pumps work in a specific direction – the substance can only enter the pump on one side and can only exit on the other side.
• One example of an active transport mechanism is the Na+/K+ pump which is involved in the generation of nerve impulses.

Question 34

Endocytosis

Answer 34

•The process by which large substances (or bulk amounts of smaller substances) enter the cell without travelling across the plasma membrane
•An invagination of the membrane forms a flask-like depression which envelopes the material; the invagination is then sealed off forming a vesicle
•There are two main types of endocytosis:
1. Phagocytosis
•The process by which solid substances (e.g. food particles, foreign pathogens) are ingested (usually to be transported to the lysosome for break down)
2. Pinocytosis
•The process by which liquids / solutions (e.g. dissolved substances) are ingested by the cell (allows quick entry for large amounts of substance)