How plants function
• Structure / function
• Resource acquisition
• Biochemistry, cell biology, molecular biology
how plants do what they do, like photosynthesis (using light energy, make
they are primary producers
how do they acquire water and minerals and other resources
how do they circulate these resources around the plant, within their structures
growth and development: occurs through signals from the environment and internal
ones (very sensitive to external signals by perceiving the environment because they do
not move and thus react to where they are to help them survive and coordinate the
stages of its life cycle with the environment)
Plant physiology: very integrative of all other types of biology, like molecular biology
microbiology, and cell biology (touches upon similar topics) while talking about plant
processes Slide 2
Plants share common ancestor with freshwater green algae
• chlorophyll a and b
• cells walls with cellulose
Evolutionary hurdles needed to make the transition to land
• water availability
(Plantae kingdom) Land plants: very large kingdom of life
This common ancestor of plants was from freshwater (aquatic)
3 major characteristics were shared between the ancestral green algae and land plants
1. Chorophyll a and b are major pigments for photosynthesis (occurs in both land plants
and green algae)…..lots of parts of photosynthesis were first elucidated in freshwater
algae such as the calvin’s cycle (using radioisotopes and paper chromatography to
determine the sequence of photosynthesis) then after being discovered in freshwater
green algae it was also seen in other plants (land plants) that similar processes were
2. Starch: major storage carbohydrate
3. Cell walls: contain cellulose (structural component) Slide 3
Some defining features of plants
1. Earth’s primary producers, converting light energy to chemical energy.
2. Non-motile, ability to grow toward essential resources, ability to acclimate
to stresses in their environment.
3. Structurally reinforced to withstand pull of gravity.
4. Mechthroughout the plant body.rals and products of photosynthesis
5. Lose water continuously therefore require effective mechanisms to attain
water and prevent water excessive water loss.
At some point ther was a movement from water to land
this generate big challenges for that transition
1. water availability is an issue (aqueous to water limiting environment) water
can often be thought of as the most limiting resource for plant growth and prouctivity in
2. gravity is another challenge, particulary for land plants which got bigger and bigger as
multicellular organisms that need structural rigidity to withstand the force of gravity (this
comes from special cell types and tissue types to provide rigidity)
The list above is from the textbook, but it’s very generic so he said he’d skip it for now
but recommended we come back to it over the course of the term as reference to further
appreciate and understand it, rather than just take them as mere generalized
That list defines plants and distinguishes them from other organisms on earth (some
deal with aforementioned evolutionary challenges) Slide 4
Classification in the plant kingdom – some basics
I. Non-vascular plants – lack xylem and phloem (eg. mosses).
II. Vascular plants
1. non-seed plants (eg. ferns).
2. seed plants.
a. gymnosperms, ~750 species (eg. conifers).
b. angiosperms, >250,000 species (the flowering plants).
i. monocotyledons (embryo with single seed leaf).
ii. eudicotyledons (embryo with two seed leaves).
aseed – a vessel containing an embryo and stored starch, protein or lipid
that acts as a source of nutrient during seed germination.
Entire kingdom can be split into two based on whether or no they are vascular
Xylem and phloem are specialized transport systems to move things around the plant
(non-vascular plants lack these) xylem moves water and minerals, phloem moves
sucrose and glucose (products of photosynthesis)
As vascular plants get bigger they need more efficient transport systems
Nonvascular plants are thus limited in the size they can achieve and stay small because
they can’t transport things aroud themselves
Vasuclar plants can be subdivided by presence of seeds
seeds= vessel that contains an embryo for the next generation that must germinate and
grow (needs a food source to draw on because it is not capable of photosynthesis , nor
is it capable yet of acquire things from the soil through roots) this stored food is also in
the seed, can be in the form of starch, protein or lipid (or a combination of them based
on what species they are)
seed composition is a species specific phenomenon
Seeds also have a hard seed coat for protection of the next generation
Seeded plants can be split as well
Gymnosperms= evergreen, small groups
Angiosperms= flowering plants (flowering is a part of their lfie cycle)
dominant group in the environment (most crops)
most studied plant processes in science (as well as this course)
Transport systems discussed in this course are mostly angiosperm systems Gymnosperms have small differences in their xylem and phloem and are less
understood because less work has been done on gymnosperms
Angiosperms can be split into two disticnt groups with distinct characteristics but the
most evident defining characteristic would be the number of juvenile cotyledon leaves
that the embryo in the seed has (one or 2) Slide 5
Unique features of the plant body
and the plant cell
Main textbook chapters: 1
(plus tutorial 1)
There is a relation between structure and function
We will cover plant cell structure (generic) and entire plant structure (like organs and
tissues) as well as plant cell types with their own function and structure
This lecture is: the Defining features of a plant cell vs. animal cell Slide 6
Plant cells are eukaryotic cells
- many of the familiar features (eg. PM, nucleus, cytosol, mitochondria,
Golgi apparatus, endoplasmic reticulum).
- but also unique & defining features such as cell wall, large vacuole, plastids.
In plant cells:
Nucleus contains genome
Cytosolic space is where various organelles are kept like mitochondria
Mitochondria carry out cell respiration (similar to the way in which animal cells do it, but
The defining features or combination of features of a plant cell include (not found in
other cells in this particular combination)
-A cell wall (some organisms have this, such as bacteria) is located outside the plasma
membrane, enclosing the cell
-Plastid organelles (types of organelles, such as chloroplast which carries out
photosynthesis) (bacteria do not have these)
-large vacuoles (gets larger as cell matures, can even be 95% of the volume, located in
the centre) pushes organelles and cytoplasm into periphery. Vacuole has a tonoplast
membrane Slide 7
Plant cell walls
Composed primarily of complex polysaccharides – but also other constituents.
Middle lamella – region “cementing” one cell wall to its neighbour.
Unlike animals, no cell migration – therefore development very dependent
upon plane of cell division and direction of cell expansion.
1 cell wall
-thin, typical of young growing cells, can stretch and expand.
2 cell wall
-found between PM and 1 cell wall
-thicker, stronger, can contain lignin for structural rigidity (eg. wood).
-simple pits to prevent blocking of plasmodesmatal connections
-found in mature cells.
Along with mostly polysaccharides Cell walls can also be made of proteins, calcium ions
and other stuff as well
cell wall is outside the PM
Middle Lamella: between cell walls of neighboring plant cells (own unique composition)
cements and positions the cells relative to one another
This means there is no cell migration (which is in animal cells) which helps in
remodelling tissues and stuff. This puts more importance on other aspects of
devlopment and modelling tissues like the plane on cell division and direction of
expansion (directions), which ultimately determine how a tissue is going to look
All plant cells have a primary cell wall good at stretching and expanding, and additional
components from inside the cell can be added to assist in stretching and expanding,
which helps after cell division when cells expand as a whole before they mature, thus
they need the cell wall to be less rigid
Secondary cell wall is only laid down in certain plant cells only after they mature
(materials for the secondary cell wall come from inside the cell), and it is made of
different things, it is stronger and more rigid (cuz of lignin) making tissues more rigid if
they have secondary cell wall
Example: Wood is made of only plant cells with secondary cell walls and lots of lignin
Once secondary wall is laid down, that cell cannot expand Slide 8
3 neighboring plant cells are shown here
First there is a plasma membrane enclosing the cell
Outside the PM is secondary wall
And outside of that is the original primary wall
Physical connections between cell walls exist and are pores called plasmadesmota,
established early in life after cell division (but sometimes establish later) and secondary
cell wall is not laid down here where these connections are formed. These pores are
simple pits, plasmodesmata Slide 9
Concept of apoplast and symplast.
This is an EMG of two plant cells on top of each other
Enclosing each of these cells is a PM and outside of each is the cell’s cell walls
between them is the middle lamella holding them in place
Many processes make use of two spaces in cells and take place in these spaces
One space is the apoplast and the other is called the symplast
Symplast: PM AND everything to th interior of the cell (cytosol, organelles, etc.)
Apoplast: cell wall, middle lamella, air space (OUTSIDE of PM) Slide 10
Plasma membrane – the ”fluid mosaic model”
-two fatty acids, glycerol, phosphate, head group.
-amphipathic (ie. hydrophobic and hydrophilic parts).
-14-24 carbons in length.d (double bonds) fatty acids, most
-↑unsaturation, ↑membrane fluidity.
-plants are poikilotherms (don’t regulate body temperature).
-at lower temperatures, plants ↑ unsaturated fatty acids to
-integral proteins (embedded, usually membrane-spanning).
-peripheral proteins (surface attachment, usually by ionic or
-anchored proteins (covalent attachment to surface lipid).
Membranes show a “sidedness” due to different components on the two sides.
Pm= fluid, bilayer and consists of lipids,
the components can move around because it is fluid, and it is a
mosaic because there are many types of components like proteins in the membrane as
well (for various functions)
The dominant lipids are the phospholipids (characteristics given above on slide)
Phospholipids are named based on the head group they have
The bilayer is both hydrophobic (interior, the fatty acid parts of the bilayer) and
hydrophilic (exterior, the outside of cell AND inside of cell because it’s a bilayer, where
the head groups point)
The head groups are usually charged, phosphates themselves are charged and water
loving, and interact with the aqueous environment
Polar/charged molecules have trouble going across the membrane because they cannot
interact with the interior hyrophobic core
The phospholipid bilayer can behave as a barrier to a lot of small molecules which is
why they have specialized transport proteins to move specific ions and molecules back
Membrane is permeable to these things unless the transporters are in place (hard to
hear at about 33:50)
There are also proteins in the membrane
Embedded proteins are on the membrane and usually span the whole membrane (from
outside to inside) Peripheral proteins are more loosely attached (by like hydrogen bonds or ionic bonds)
Anchored proteins are stuck to special lipids in the membrane Slide 11
Fatty acids are in the interior, and the phosphate heads are to the aqueous exteriors
(both outside and inside the cell)
Core is hydrophobic and hydrofilic exterior to the membrane
There are integral and peripheral proteins
Basically describing all the aspects we talked about earlier Slide 12
hydrophobic FA- varies in length and saturation (presence of double bonds)
unsaturated= has a double bond, has a kink in it’s chain which means the Fatty acid
allows for a more fluid membrane
The fluidity of the membrane changes as a function of the temperature
(plants do not regluate their temperature, they just use the ambient temperature)
Temperature dictates metabolism as well as membrane fluidity
To maintain an optimal fluidity in the membrane they change the fatty acid chains (to be
more saturated or unsaturate depending on the seasonal temperature)
Membrane is NOT static, both protein and fatty acid composition changes over time
Different membrane compositions for various parts such as the mitochondrion or plastid,
or amongst various cell types and function Slide 13
Some are in cytosol, or can be in the exterior (apoplastic)
Anchored in place by specific lipids embedded in the bilayer
Plastid membranes have no phospholipids, even though they are usually dominant for
most membranes, instead they have lipids in with heads groups that don’t have
phosphates, but rather a sugar called galactose (or derivatives thereof) Slide 14
-single membrane bound (ie. one bilayer), membrane the vacuole is
called the tonoplast.
-young cells have small provacuoles derived (pinching off) from the Golgi.
-as cell matures, provacuoles fuse and gets bigger
-in mature cells, the vacuole can be up to 95% of total cell volume.
-vacuoles can be important store of water, inorganic ions, organic acids,
sugars, enzymes, secondary metabolites (diverse functions).
-it is primarily water uptake into vacuoles that drives cell expansion and
generates turgor pressure.
Single membrane= One bilayer (some other organelles may have 2 bilayers, such as
the mitochondrion or plastids)
Many things are found in the vacuole, it is not inocuous, aside from a majority of the
cell’s water there are many inorganic ions, organic acids, sugars, enzymes to catalyze
particular biochemical reactions, and also there are secondary metabolites (not the
primary metabolites that help with many processes like respiration, calvin cylcle, and
etcetera) but rather they are specific to plants and through secondary metabolism they
make many compounds like nicotine, caffeine and such (things that impact other
organisms, like animal nervous systems)
These secondary metabolites (caffeine, nicotine, etc.) act as a defense against other
organisms such as pathogens (to deter disease from fungi, bacteria and stuff) and to
decrease susceptibility to being eaten by herbivores and insects
Therefore these compounds (the secondary metabolites) behave as chemical warfare
for the plants that come as a result of secondary metabolism, and they are stored in the
vacuole (because they may be too toxic to the plant to store in the cytosol or other
As the plant cell takes up more water, it exapnds and pushes against the cell wall which
drives cell expansion (the stretching of the primary cell wall) by overcoming the force of
the cell wall. This is done by water influx into the cell by osmosis
If the cell wall can resist being expanded, it’ll push back a bit and have the potential to
build this positive turgor pressure to expand (not seen in animal cells, because if they take in too much water by osmosis they just burst since they cant resist the expansion
like plant cells can by the cell wall) Slide 15
-protein storing vacuoles and lytic vacuoles are abundant in seeds. During
germination these fuse, and the proteases break down the proteins to
provide nutrient for the young seedling.
-senescence is the programmed death of plant organs (eg. leaf senescence).
As part of this program, vacuoles release hydrolytic enzymes (proteases,
ribonucleases, glycosidases) that degrade macromolecules to small
molecules. These small molecules can then be re-mobilized to other parts
of the plant rather than being lost.
Seeds store food for the next generation (young embryo), maybe in the from of starch or
The protein stored in the seed is in a special protein storing vacuole
During germination, this protein storing vacuole fuses with another vacuole (called the
lytic vacuole) that contains a lot of proteases (enxymes that break a protein down to it’s
constituent amino acids) and these stored proteins are used by the embryo by having
these vacuoles fuse and the proteins in the large vacuole broken down to its Amino acid
components that can readily be distributed to different parts of the embryo
Different organs (like flower and leaves) under go senescene (programmed death) like
leaves in the fall as they change color (the important macromolecules of the leaves,
such as DNA, lipid, proteins are all being borken down to the constituent components
which are transportd out to other parts of the plant to be saved and not lose nutrients
when the leaf falls off )
Proteins have lots of nitrogen, which is one of the most limiting nutrients in the
environment for plant growth, so once it is absorbed plants try to hold on to it as long
they can and not waste it, thus they recall and remobilize it from the leaves during the