Topic 3 - Organisms Exchange Substances With Their Environment

Question 1

Absorption of lipids from the lumen into lymphatic system (6)

Answer 1

.Lipid broken down into glycerol, fatty acids and monoglycerides
.Fatty acids + monoglycerides associate with bile salts to form micelles
.Micelles are water soluble and get transported to epithelial cell where they can diffuse in

.Once in cell, ER converts broken down lipid into triglycerides
.ER and Golgi combine triglycerides with proteins, forming chylomycrons
.Chylomycrons are packaged into vesicles and released into the lymphatic system via exocytosis

Question 2

Explain the impact of size on metabolic rate

Answer 2

.Smaller organisms have larger surface area to volume ratio
.So faster heat loss in relation to body size
.Faster rate of respiration/metabolism releases heat

Question 3

What happens to haemoglobin once blinded to first oxygen

Answer 3

Cooperative binding where haemoglobin changes shape after binding to the first oxygen, making it easier to bind to further oxygens

Question 4

What is the Bohr effect and how does it effect the dissociation of oxyhemoglobin

Answer 4

.This is the impact of carbon dioxide concentration,
.Causes affinity of haemoglobin to decrease (curve shifts to the right), due to CO2 decreasing PH of blood, causing haemoglobin to change shape making it harder for oxygen to bind but makes it easier for oxygen to unload. Occurs near respiring tissues.

Question 5

How can Haemoglobin be adapted to different organisms

Answer 5

Low oxygen concentration in environment - High affinity to load oxygen more readily
High metabolic rate - Low affinity to unload oxygen to respiring tissues more readily

Question 6

What 3 factors make up cohesion-tension theory

Answer 6

Cohesion - water is DIPOLAR enabling HYDROGEN BONDS creating COHESION so water moves up in a CONTINUOUS WATER COLUMN.
Capillarity- Water adheres to xylem walls, the narrower the xylem , the bigger impact of capillarity ( more water can stick so it moves up more without any pull action)
Root pressure - as water moves into roots via osmosis, volume increases, therefore causing pressure in the roots to also increase, so root forces water upwards (positive pressure resulting in a pushing action).

Question 7

Explain why water moves up the xylem (5)

Answer 7

.Water vapour EVAPORATES out stomata, loss is volume lowers pressure
.When this water is lost via TRANSPIRATION more water is pulled up to replace it (negative pressure)
.Due to HYDROGEN BONDS between water molecules they are COHESIVE, creating a CONTINUOUS COLUMN OF WATER
.Water molecules ADHERE to walls of xylem (makes water less likely to fall down due to force of gravity)
.As water is pulled up the xylem, this creates TENTION, pulling the xylem in to become narrower (increasing capillarity further)

Question 8

Function of the Phloem and Xylem

Answer 8

Xylem - transports water from the roots to the leaves for transpiration
phloem - Transports organic substances made in the leaf in photosynthesis (E.g Sucrose) around the plant enabling them to respire or to store as insoluble starch

Question 9

Adaptations of the phloem (3)

Answer 9

Sieve tube elements -
.Perforated end walls for continuous flow of organic substances
.Very few organelles (no nucleus) so that there is a hollower tube

Companion cells -
.Provides ATP to actively transport organic substances

Question 10

How is the pressure gradient maintained in Mass flow for plants

Answer 10

.At sink cells, sucrose is used in respiration/to produce insoluble starch
.Sucrose actively transported sink cell, reducing water potentially

Question 11

Explain the process of translocation from source cells

Answer 11

1) PHOTOSYNTHESIS occurring in chloroplast of leaves CREATES ORGANIC SUBSTANCES
2) SUCROSE is ACTIVELY TRANSPORTED into phloem (sieve tube element) using COMPANION CELLS
3)Increased sucrose in phloem LOWERS WATER POTENTIAL
4)Water moves into phloem from the XYLEM via OSMOSIS, increasing the HYDROSTATIC PRESSURE
5) Water potential near sink cells

Question 12

How can we investigate Translocation (2)

Answer 12

Tracers - isolate plant and provide with only radioactivity labelled CO2, once absorbed via stomata , plant will use this CO2 in photosynthesis and produce radioactively labelled sugars. When exposed to x-ray film, the carbon turns black, allowing us to locate where the sugars are , and where they’re being transported to.
Ringing experiment- Ring of bark and phloem are removed from tree, and overtime the parts above the ring will swell due to sugary solution not being able to be transported down sink cells