| Describe how salts are reabsorbed against a concentration gradient. | (by) active transport ;
from a low to a high concentration / AW ;
(through cell) membrane ;
ref. to proteins (pumps / channels / AW) ;
uses energy ;
from respiration ; |
| Table 3.1 also shows that water is reabsorbed in the kidneys of both humans and mice.
State the name of the process that mammals use to reabsorb water. | osmosis. |
| Transmission of impulses relies on the flow of ions through the cell membranes of neurones down their concentration gradients. Active transport is responsible for maintaining the concentration gradients of ions across the membranes of neurones.
Explain how ions are moved across membranes by active transport. | involves, proteins / carriers / pumps (in neurone membrane) ;
(named) ion(s) bind to, proteins / carriers / pumps, to move ions / AW ;
move ions, against concentration gradient / from low to high
concentration ;
using energy ;
AVP ; e.g. change in shape of carrier (protein) |
| Ions move into guard cells by active transport.
Describe how the ions move into the guard cells | move against the concentration gradient ;
proteins (in membrane) ;
using energy ;
from respiration ; |
| Describe how nitrate ions enter the roots of plants | root hairs ;
(by) active, transport / uptake ;
across (cell) membranes ;
against a concentration gradient / low to high concentration / AW ;
by proteins (molecules / pumps / carriers) ;
use of, energy / ATP ;
(also by) diffusion ; |
| The researchers thought that capsaicin stimulated receptors in the skin.
Explain the process by which capsaicin could reach these receptors | diffusion ;
down concentration gradient / high to low concentration ;
active transport ;
through epidermis ;
between / into / through, cells ;
across cell membranes ;
AVP ; |
| State the name of the process that moves mineral ions into root hair cells through cell membrane proteins. | active transport |
| Explain how protein molecules move ions across a membrane during this process. | 1 protein uses, energy / ATP (from respiration) ;
2 idea of protein interaction with ions ;
3 (to) change shape of protein ;
4 ions move through the protein ;
5 against concentration gradient / lower concentration to high concentration
(across a membrane) ;
6 AVP ;e.g. ref to selective / specific shape |
| Rhabdostyla is a single-celled organism that has no cell wall and no chlorophyll.
Gases are exchanged across the cell membrane of Rhabdostyla.
Name:
(a)
the gas produced by Rhabdostyla .................................
the process that produces the gas ...................................................................................
the method of removal of the gas ..................................................................................... | carbon dioxide/CO2 ;
(aerobic) respiration ;
simple diffusion |
| Explain, using the term water potential, why Rhabdostyla needs to remove excess water. | water enters by osmosis ;
down a water potential gradient/high(er) to low(er) water potential ;
through partially permeable membrane ;
needs to remove water to prevent bursting ; |
| Explain the results shown in Fig. 4.2 | as concentration of sea water increases the removal of water decreases ;
as concentration of sea water increases the water potential gradient
decreases ;
therefore less water enters at higher concentrations of sea water ;
less excess water ; |
| The contractile vacuole removes excess water.
Single-celled organisms with cell walls do not have contractile vacuoles. Suggest why | cell walls, inelastic / do not stretch/rigid/ inflexible/ keep shape of cell ;
cells, are turgid/ have high turgor pressure ;
resist any increase in, volume/ pressure ;
these cells do not absorb excess water ;
the cells will not burst ; |
| Define the term osmosis. | movement/ diffusion, of water (molecules) ;
from high water potential to low water potential/down water potential
gradient ;
across a partially permeable membrane ; |
| Predict which of the liquids would cause the largest decrease in mass of a potato stick. | 1.0 (mol dm–3 sodium chloride solution) ; |
| The students dried the potato sticks with paper towels before putting them on the
electronic balance.
Suggest why. | (to remove) excess / surface/AW, water/AW, on potato sticks ;
to measure the mass of the potato (stick) only ; |
| After the experiment the students noticed that the potato stick with the lowest mass was soft and floppy.
Explain why the potato stick had become soft and floppy. | cells / potato sticks, have lost water (by osmosis) ;
from high water potential to low water potential/down water potential
gradient ;
(cells / tissue/ potato) were, plasmolysed/ flaccid ;
loss of turgor (pressure) ;
not enough pressure of water pushing on cell walls ; |
| The students followed the same experimental procedure with boiled potato sticks and found no overall change in mass in any of the solutions.
Suggest why the mass of the boiled potato sticks remained the same. | protein denatured (when cooked) ;
cell membrane, damaged/destroyed (when cooked) ;
no osmosis will occur ; |
