January 2009 Bio Unit 1

Question 1

Explain, using the term water potential, what has happened to cell M. (3)

(cell M is a flaccid plant cell)

Answer 1

water moves out of cell ;
by osmosis ;
cell has, higher / greater / less negative, water potential (than
surrounding solution) / ORA ;
(water moves) down water potential gradient/from high to low water potential ;

Guidence 
DO NOT ACCEPT across or along water potential
gradient
DO NOT ACCEPT ref to water concentration
anywhere
IGNORE ref to solute potentials

Question 2

Outline the ways in which substances, other than water, can enter a cell through the plasma (cell surface) membrane. (6)

• small substances
• large substances
• polar substances

Answer 2

diffuse (through membrane / phospholipid bilayer) ;
large substances
(using), transport / carrier, proteins ;
endocytosis / phagocytosis / described ;
polar substances
through, pore / channel, proteins ;
(using), transport / carrier, proteins ;
general – must be used in correct context, each once only
ref to facilitated diffusion ;
ref to active transport / use of ATP ;

Question 3

State what is meant by the term stem cell

Answer 3

a cell that is, unspecialised / not differentiated ;
capable of, division / mitosis ;
able to, differentiate / specialise / become other cell types ;

Question 4

State three reasons why mitosis is important to organisms (3)

Answer 4

1. growth (of tissue / organism) ;
2. replace (cells) / repair (tissues) ;
3. asexual reproduction/cloning / producing genetically identical cells ;
4. maintain chromosome number in all cells ;

Question 5

Describe how the action of the heart is initiated and coordinated.(5)

Answer 5

T / SAN, creates / initiates / starts / originates, excitation ;
wave (of excitation) spreads over atrial, wall / muscle ;
ref to, AVN / U ;
atria contract / atrial systole ;
contraction is synchronised / AW ;
delay at AVN ;
(excitation spreads) down septum ;
ref to, bundle of His / Purkyne fibres ;
ventricles contract / ventricular systole, from, apex / bottom ;

Guidence
DO NOT ACCEPT electricity / signal / message
DO NOT ACCEPT if response suggests that brain
needed to trigger SAN

Question 6

Research using carbon dioxide containing a radioactive label, C14, has revealed the following
evidence about the mechanism of translocation:
A labelled carbon can be observed in the phloem soon after being supplied to a well-lit
plant;
B the rate of movement of sugars in the phloem is many times faster than could be achieved
by diffusion alone.
Different research has revealed that:
C an insect such as an aphid feeds by inserting its proboscis (mouth parts) into the
phloem;
D the pH of the phloem companion cells is lower than surrounding cells;
E the phloem companion cells contain many mitochondria.

Using the letters A, B, C, D and E, select two pieces of evidence from the list above which
support the theory that translocation occurs in the phloem.

Answer 6

A / labelled carbon can be observed in the phloem soon after
being supplied to the plant ;
B / the rate of flow of sugars in the phloem is higher than
diffusion ;
C / an insect such as an aphid feeds by inserting its proboscis
(mouth parts) into the phloem ;

Question 7

State what is meant by the terms source and sink

Answer 7

source
site where, sucrose / sugars / assimilates, loaded (into phloem)
/ AW ;
sink
site where, sucrose / sugars / assimilates, unloaded / removed
(from phloem) / AW ;