lab exam 2

photosynthesis overview

1. photon absorbed

2. energy transferred through antenna complex

3. reaction center chlorophyll excited

4. electron passed to primary acceptor

5. electron enters transport chain

electron flow types

Photosystems:

• photosystem I (PSI): contains P700

• photosystem II (PSII): contains P680

Linear flow: H₂O→PSII→ETC→PSI→NADP+

• produces ATP + NADPH + O₂

Cyclic flow: PSI→ETC (cycle)

• produces ATP only

Photophosphorylation

ATP synthesis driven by light energized electron transport

Electron transport builds H+ gradient

ATP synthase converts proton motive force to ATP

three phases of the calvin cycle

1. carbon fixation: CO₂ + RuBP → 3PGA

2. reduction (per molecule of 3PGA): 3PGA + ATP + NADPH → G3P + ADP + NADP⁺

3. regeneration: (per 3 turns): 5G3P + 3ATP→ 3RuBP + 3ADP

key enzyme in photosynthesis

Rubisco

catalyzes CO₂ fixation in the calvin cycle

binds O₂ leading to photorespiration

enzyme activity is stimulated by ATP and NADPH produced by light reactions

• central enzyme to global food production

photorespiration

rubisco enzyme can bind CO₂ or O₂

• CO₂→carbon fixation

• O₂→photorespiration

strategies to reduce photorespiration

• C3: rubisco fixes CO₂ directly in mesophyll cells

• C4: CO₂ is released in bundle sheath cells

• CAM: CO₂ is stored as organic acids

meiosis

• used for sexual reproduction

• 2 divisions to 4 genetically different haploid cells

• chromosome number is reduced by half 2n→n

• cells develop into eggs or sperm

meiosis 1 (draw)

• homologous chromosomes separate

• crossing over occurs in prophase 1 to create new combinations of alleles

• homologous pairs align randomly during metaphase 1 (aka independent assortment)

meiosis 2 (draw)

• resembles mitosis

• sister chromatids separate

• results is 4 haploid cells

haploid vs diploid cell

diploid (2n)

• two sets of chromosomes

• 46 total chromosomes in humans (23 pairs)

• somatic cells

haploid (n)

• one set of chromosomes

• 23 total chromosomes in humans (46/2 after meiosis 1 and 2)

• gametes

nondisjunction

the failure of chromosomes to separate correctly

results in gametes that are chromosomally imbalanced

aneuploidy: a gamete that has an extra number of chromosomes or missing chromosomes

nondisjunction in meiosis 1 vs meiosis 2

meiosis 1: 2 monosomic zygotes and 2 trisomic zygotes

meiosis 2: 2 normal zygotes, 1 monosomic zygote, and 1 trisomic zygote

interphase (and draw)

G1: cell growth

S: DNA replication

G2: additional growth and preparation for division

prophase (and draw)

chromosomes condense

nuclear envelope present, begins breaking down

spindle forms

metaphase (and draw)

chromosomes line up at the metaphase plate

spindles attach to kinetochores

no nuclear envelope

anaphase (and draw)

sister chromatids separate

chromatids are pulled to opposite poles

no nuclear envelope

telophase (and draw)

chromatids reach poles

nuclear envelope reforms

chromosomes decondense

cleavage furrow divides the cell

cytokinesis (and draw)

cytoplasm divides

two identical daughter cells

mitosis

used for growth, repair, and cell replacement

1 division to 2 genetically similar cells

chromosome number stays the same: 2n→2n

cytokinesis in plant vs animal cells

plant cells: vesicles transport cell wall material to the middle of the cell to form a cell plate between nuclei

animal cells: a cleavage furrow deepens until the cell divides. Actin and myosin constrict the cell membrane

mitotic index

the percent of cells in a region that are undergoing mitosis

(total cells in mitosis / total cells counted) x 100

pigments

nonpolar, and located in the thylakoid membranes of chloroplasts

used to absorb energy from the sun

• chlorophyll A, directly involved in converting light energy to chemical energy, releases O₂ as a byproduct

• chlorophyll B (accessory pigment), light harvesting pigment that transfers its energy to chlorophyll A

• carotenoids (accessory pigments) (carotenes and xanthophylls), acts as antioxidants to protect chlorophyll molecules from photooxidative damage

Rf value

the ration of how far the substance migrated up the chromatography paper compared to the distance migrated by the solvent

(distance of the top of the target band) / (distance of the highest band)

epidermis

• one cell layer thick

• secretes a waxy cuticle that retards the loss of water

• includes the upper epidermis and lower epidermis

stomata

located in the lower epidermis

where gas exchange with the atmosphere can occur

guard cells

in each stoma

regulate the opening and closing of stoma

mesophyll

between the two layers of the epidermis

most photosynthesis occurs here

palisade mesophyll: consists of long cylindrical, relatively closed packed cells\

spongy mesophyll: contains spaces between cells for temporary storage of gases

veins

the medium in which water is supplied

contains special conducting tissue called xylem and phloem

xylem: conducts water from the roots to the leaf

phloem: distributes organic products of photosynthesis and other substances to areas of the plant where they are needed

cell fractionation

isolates and purifies cellular components by cellular disruption and differential centrifugation

the steps of the scientific method

1. make an obersvation

2. form a hypothesis

3. make a prediction

4. preform an experiment

5. gather data

6. analyze findings

7. draw a conclusion

falsiability

hypothesis must be falsifiable; if they are not true, they can be determined to be false

testing a hypothesis

factors:

• independent variable: the experimental variable that changes

• dependent variable: how the variable reacts to that change

• null hypothesis: the default hypothesis

• alternative hypothesis: the hypothesis that counters the null hypothesis

interpolation vs extrapolation

interpolation: between measured points on a graph

extrapolation: goes beyond the experience with an experiment