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Unit 3: Cellular Energetics


Extracellular Components

Extracellular components and connections between cells help coordinate cellular activities
Most cells synthesize and secrete materials that are external to the plasma membrane
These extracellular (outside plasma membrane) structures include
Cell walls of plants- major structural component of plant cells made of cellulose, also found in prokaryotes, protists and fungi (peptidoglycan)
Cell wall protects the plant cell, maintains its shape and prevents excessive uptake of water
Plant cell walls are made of cellulose fibers embedded in other polysaccharides and proteins
Thin Flexible Primary Cell Wall
Thick Secondary Cell Wall
In between plasma membrane and primary wall gives structural integrity
Middle lamella - material between cell walls
Plasmodesmatagaps in cell wall allowing for communication and movement of things between plant cells, rigid cell walls are restrictive unlike permeable membranes
Extracellular matrix (ECM) of animal cells instead of cell walls
Series of glycoproteins such as collagen (major), proteoglycans, and fibronectin make up ECM
Fibronectin connects collagen to integrin
Proteoglycans perform adhesion (glue)
Proteins bind to receptor proteins in the plasma membrane called integrins
Intercellular junctions physically connect cells, adhere interact or communicate through direct contact
Plasmodesmatagap-like channels that perforate cell walls
Tight Junctions membranes of neighboring cells are pressed together preventing leakage of extracellular fluid in between cells (in stomach)
Desmosomes (anchoring junctions) fasten cells together into strong sheets--strongest function (muscle cells)
Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells (heart cells), enable multiple cells to act as one


The most important reaction in all of nature, makes food
Converts solar energy into chemical energy
Directly and indirectly nourishes all living things
Autotrophs/Producers - organisms that produce their own food through photosynthesis
Algae (protist, eukaryotic organism), plants, cyanobacteria - first living organisms to perform photosynthesis
Heterotrophs/Consumers - must eat in order to obtain energy, eating products of photosynthesis
Energy (light, invested energy) + 6CO2 + 6H2O → C6H12O6 + O2
Opposite of cell respiration (which is exergonic, produces ATP), photosynthesis is endergonic
Water is oxidized to O2, CO2 is reduced → glucose
Photosynthetic part of a plant (organ): Leaf
Holes in leaf: stomata, where water evaporates (transpiration) and CO2 enters and O2 leaves
Creates transpirational pull from roots
Xylem are cells that water travels through
Plants want water to evaporate out of the plants, no transpirational pull without evaporation
Plant would dehydrate if too much water evaporated, need to balance transpiration
Increase transpiration and dehydration
Heat (temperature)
Dryness (humidity)
STOMATA CLOSE to balance out environment with the guard cells
Calvin Cycle cannot occur (no CO2) can’t make sugar
RuBisCo can ALSO fix O2 to RuBP in place of CO2 → cant produce G3P
Wastes NADPH and ATP
C3 Plants make 3-Carbon compound, PGA in the calvin cycle
C4 Plants live in dry conditions (midwest), have adaptations to prevent photorespiration → STORE CARBON DIOXIDE
Doesnt matter if stomata are closed or open
Used stored CO2,
C4 Plant
Uses enzyme PEP Carboxylase → pulls in CO2 stores carbon as 4 carbon molecule Oxaloacetate
Calvin cycle takes place in Bundle-sheath cell, but still have mesophyll cells
CAM Plant - the extremes (cacti, desert plants)
Store carbon as crassulacean acid, organic acid
CAM Plant opens stomata at night (when it cools down)
More stomata on bottom, if more on top plant would dehydrate
Guard cells: flank stomata, control if stomata are open, closed, where gasses enter and leave, (O2/CO2), water can evaporate out of the stomata → transpiration (transpirational pull)
Mesophyll- part of a leaf that contains lots of photosynthetic cells
Cells contain chloroplast - double membrane, inside are pancake shaped discs called thylakoids, and stacks of thylakoids = granum
Fluid in membrane outside thylakoids called stroma
Two reactions:
Light Reactions - light (photo) inside the thylakoids
NADP+ and ADP + P, take H2O and oxidize it, produce NADPH, and ATP, O2 as a byproduct,
Light to make ATP - photophosphorylation
Calvin cycle (The Dark Reactions)- synthesis (builds molecule) inside stroma
Major reactant in cycle: CO2 reduced and given electrons/protons, creates glucose, given by NADPH gives CO2 the electrons/protons. Electrons - energy
Powered by ATP
Purpose of producing glucose?
Glucose is used for everything:
Sugar → cell respiration, used to make ATP to grow plant
Sugar = structure, cellulose (long chain of glucose)
Sugar = energy storage, starch
Light - electromagnetic radiation
Shorter wavelength -- high energy (UV, gamma, X ray)
Longer wavelength -- low energy (infared microwaves, radiowaves)
Different colors correspond with different wavelengths, visible light in the middle of spectrum
Chlorophyll a is the main photosynthetic pigment
Accessory pigments such as chlorophyll b broaden the spectrum used in photosynthesis
Xanthophylls - yellow
Carotenoids - orange
Reflect (bounce off) vs Transmitting (go through)
No light is absorbed by cell
Green light cannot be used by plant, would die
Plants absorb red and blue light the best
Color of sky depends on molecular composition of atmosphere
Spectrophotometer - put sample of light in, tells level of transmittance or absorption
Shoot green light through chlorophyll, high transmittance (low absorption)
Shoot blue light through chlorophyll, low transmittance (high absorption)
Absorption Spectrum - graph plotting a pigment’s light absorption versus wavelength
Larger spectrums,
Action Spectrum - profiles the relative effectiveness of different wavelengths of radiation in driving a process, totality of spectrums
Pigment - molecule that will absorb or reflect a wavelength
Color determined by what it reflects
Trees go dormant in winter, chlorophyll dies, only see carotenoids and xanthophylls (yellow + orange), not enough sunlight
Engelmann’s Experiment
Grew algae under different wavelengths
Grew aerobic bacteria on top of the algae, large growth on opposite sides of spectrum, none in green because algae isn’t photosynthesizing there
Plants not black because would absorb every wavelength, overheat, proteins denature
Chlorophyll has a Magnesium center (a vs. b has difference of one func. group)
Mg holds on to electrons, electrons from water and NADPH
Accepts unit of light - photon, excites electron, gives power to electron

Cellular Respiration

Alcohol fermentation (yeast)
Pyruvate converted to ethanol (2 carbon, releases CO2)
Brain cells = purely aerobic
Obligate anaerobes = die in the presence of O2 (bacteria), carry out fermentation/anerobic respiration
Denitrifying bacteria
Anaerobic respiration: use sulfates as final electron activity instead of O2 and substrate level phosphorylation not the electron transport chain
Oldest process
Before mitochondria, glycolysis took place
Oldest prokaryotes used this for energy
Cell respiration
Regulated by feedback inhibition
When ATP builds up, pathway is turned off
Utilizes allosteric enzymes
Turns off Phosphofructokinase (first enzyme in pathway)
AMP turns back on, forces pathway on

Fats and proteins can also be used in cellular respiration (triglycerides), not just glucose and carbohydrates
Fats provide more energy than carbohydrates, therefore more ATP
Glycerol (3 carbon molecule) and three fatty acids
Monomers of fatty acids/glycerol can enter cellular respiration
Glycerol has the same amount of carbons as a glucose pyruvate, enters process at pyruvate oxidation no need for glycolysis, more energy
Beta Oxidation
Fatty acids from lipids need to break down long chains of carbons in order to enter cellular respiration
Breaks the fatty acid chain and breaks it down into two-carbon molecules
Feeds directly into the Kreb Cycle
If you don’t have enough carbs or lipids, or too much protein, protein can be used in cellular respiration
Proteins have an atom that cannot enter cellular respiration, have to get rid of nitrogen in order to enter, stomach and small intestines break down proteins into amino acids
The amino acids can go into cellular respiration
The process by which the amino group (NH2) leaves the amino acid to enter cell respiration
Amino acid can enter multiple levels of the cellular respiration
Cellular Respiration refers to both aerobic and anerobic respiration but is mainly the aerobic respiration
Respiration usually tracked with glucose because it starts at the first step
Fermentation partial degradation of sugars that occur without O2
Keeps pyruvate happening?
Aerobic respiration consumes organic molecules and O2 and yields ATP
Anerobic Respiration similar to aerobic respiration but consumes compounds other than O2
Glycolysis occurs whether or not O2 is present


All plants evolved from a type of green algae called carophycenes, but modern plants are different (derived character) they can live on land
Evolutionary History: chronologically
Bryophytes: mosses, first group to evolve
Pteridophyta: ferns
Vascular Tissue: next derived character (xylem= water transport, phloem=sugar transport)
Evolution of Seed Plants: (MAJOR)adaptation that allows plants to no longer rely on water to reproduce → reproduce on land more
Gymnosperms: use cones as a reproductive structure, rely on wind to carry pollen from cone to cone
Angiosperms (flowering plants): produce flowers (reproductive structure)
Alternation of Generations:
Every generation plants flip between haploid to diploid and then back
Sporophyte: (2n) goes through meiosis to make haploid spores
Gametophyte: (n) goes through mitosis to make gametes, create a diploid zygote
In ANGIOSPERMS, the sporophyte version is dominant whereas the gametophyte is extremely reduced
The Flower: used to reproduce in angiosperms, help from animals, wind, and insects to transport pollen, brightly colored to attract other animals/bugs to it
Nectar: sugary substance produced by flowers to attract birds and bees to consume, the pollen will stick to the animals so pollen can go from plant to plant
Contains both male and female reproductive parts (lilies) but most flowers are either male or female
Stamen: male reproductive part
Anther: structure that produces pollen, flower is the sporophyte, whereas pollen produced has two male gametophytes (sperm)
Filament: long stalk that comes out of the anther
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