Lecture 12: Gas Exchange in Plants

Question 1

what is diffusion?

Answer 1

movement of a population of molecules from an area of high concentration to an area of low concentration without the use of energy

Question 2

simple diffusion vs facilitated diffusion?

Answer 2

simple diffusion occurs when molecules move down their concentration gradient across a plasma membrane with no help needed. facilitated diffusion occurs when molecules move down their concentration gradient with the help of a transport protein

Question 3

what is tonicity?

Answer 3

the ability of a surrounding solution to cause a cell to gain or lose water

Question 4

what affects diffusion of molecules across a membrane?

Answer 4

1) concentration gradient: greater the difference in concentration will increase diffusion rate
2) temperature: higher temperature increases molecular movement increasing diffusion rate
3) molecular mass: bigger will diffuse slower than smaller molecules
4) solubility: polar/nonlipid will diffuse slower
5) membrane thickness: thicker membrane will take longer
6) membrane surface area: more space the faster the rate of diffusion
7) distance travelled: limit on how far molecules can efficiently travel

Question 5

why is diffusion not efficient over long distances?

Answer 5

a large spherical cell will die from lack of nutrients and lack of waste removal since it will take too long for things to move to and from the centre of the cell

Question 6

do smaller or larger organisms have a large surface area to volume ratio?

Answer 6

smaller organisms have a larger surface area to volume ratio = meaning more space for molecules to pass meaning higher diffusion ALSO irregularly shaped cells also have more sa:v ratio: ALSO flattened shapes have greater surface area as well

Question 7

what is gas exchange?

Answer 7

gas exchange is the process by which organisms uptake gasses essential for physiological processes and release waste gasses as a byproduct of those processes

Question 8

what gasses do animal cells uptake and release?

Answer 8

uptake: o2 and release: co2

Question 9

what gasses do plant cells uptake and release?

Answer 9

uptake: o2 and co2 and release: o2 and co2

Question 10

do plant cells do photosynthesis or cellular respiration?

Answer 10

they do both but photosynthesis faster than cellular respiration= producing more oxygen than needed

Question 11

what is involved in photosynthesis vs cellular respiration?

Answer 11

photosynthesis: sunlight, h2o, and co2 producing o2 and glucose
cellular respiration: oxygen and glucose producing co2, water, atp

Question 12

light compensation point?

Answer 12

light intensity where the rate of photosynthesis matches the rate of cellular respiration leading to the net production of oxygen being 0

Question 13

what method do plant cells use to exchange co2 and o2 with the environment?

Answer 13

simple diffusion, o2 and co2 are small onpolar molecules that can move down their concentration gradient across the plasma membrane without the use of energy, plants also have plasmodesmata which are small perforations in cell wall that allow molecules pass in easily

Question 14

do all the cells inside the tree trunk perform gas exchange?

Answer 14

all living cells must perform gas exchange. but no not all cells inside the tree trunk perform gas exchange because xylem die at maturity

Question 15

what are the 3 main organs in plants?

Answer 15

roots, stems, leaves

Question 16

each organ in the plant has?

Answer 16

specialized structure in the dermal tissue to perform gas exchange with the environment

Question 17

what are the specialized structure in each of the organs?

Answer 17

root: root hairs are thin projections at the tips of roots that increase the surface area and also function in anchoring the plant. also not covered in waxy cuticle
stem: in woody plants the epidermis is called the periderm and has lenticles where the gases exchange. they also dont open and close. in non woody plants: the epidermis has stomata
leaves: have stomata that open and close and gas exchange occurs there and also it is where 95% of water evaporation occurs

Question 18

what are guard cells?

Answer 18

stomata are flanked with guard cells that control the opening and closing of the stomata. they also change shape with water loss/uptake.
when theyre open and letting water in, they become turgid and bow outwards but when closed and not letting water and gas in, they become flaccid and droop inwards

Question 19

what causes stomata to open and close?

Answer 19

open: exposure to sunlight and with low co2/high o2
close: dry soil

Question 20

explain leaf structure in regards to sa:v ratio and tissues

Answer 20

leaves have a high surface area to volume ratio for gas exchange to occur.
they have 3 types of tissues including dermal, vascular, and ground tissue
dermal tissue: has stomata and guard cells. can be at the top and bottom of leaves
vascular tissue: leaf veins have xylem and phloem that transport sugar and water close to the place of photosynthesis
ground tissue: mesophyll is the ground tissue between the two layers of dermal tissue. mesophyll is mostly made up of parenchyma cells. the mesophyll is split into 2 layers including palisade and spongy. palisade is mostly made up of parenchyma cells and located at the upper part of leaves and contains the most chloroplasts. the spongy mesophyll has many air sacs in the cell for gas to circulate and it is located below the palisade