DAT Photosynthesis and Cell Div.

Question 1

Photosynthesis:

Answer 1

biological process done by
photoautotrophs (plants, some bacteria and protists);
captures energy from sunlight and converts it to chemical
energy stored in the form of glucose
* Takes place in the chloroplast
* Overall Reaction: 6CO2 + 6H2O → C6H12O6 + 6O2

Question 2

Chloroplast:

Answer 2

organelle that is only found in
photoautotrophs; contains chlorophyll (light absorbing
pigment with a porphyrin ring that has an Mg atom in the
center; similar structure to hemoglobin)

Question 3

Chloroplast Structure (external to internal):

Answer 3

1. Outer membrane (smooth)
2. Intermembrane space
3. Inner membrane (smooth)
4. Stroma (cytoplasm of chloroplast)

Question 4

Stroma Structure

Answer 4

a. Stroma lamellae: connect thylakoids together
b. Thylakoids: membrane bound flattened disks
found in the stroma
i. Thylakoid membrane: contain chlorophyll
ii. Thylakoid lumen: space enclosed by
thylakoid membrane
iii. Granum: stack of thylakoids

Question 5

Photosynthesis includes…

Answer 5

light dependent and independent rxns

Question 6

Light-Dependent Reactions:

Answer 6

include cyclic and noncyclic
photophosphorylation using chlorophyll found in
photosystems

Question 7

Photosystems (PS):

Answer 7

(PS): large chlorophyll containing
proteins found in the thylakoid membrane.

Question 8

Action Spectrum

Answer 8

plots wavelengths of light that are
most effective at causing photosynthesis

Question 9

Red/blue light:

Answer 9

highest rate of photosyn

Question 10

Green light:

Answer 10

lowest rate of photosynthesis (chlorophyll
reflects green wavelength of light instead of absorbing
it; this is why plants are green)

Question 11

Noncyclic Photophosphorylation

Answer 11

1. Sunlight hits PS II → photons from light excite
   electrons (boosts electrons to higher energy level)
2. High energy electrons passed to primary electron
   acceptor
3. Primary electron acceptor passes electrons through
   the electron transport chain (ETC), pumps protons
   (H+) against concentration gradient from stroma ➞
   thylakoid lumen (creates an electrochemical
   gradient)
4. Protons flow through ATP synthase down their
   concentration gradient, catalyzing the conversion of
   ADP to ATP
   a. This ATP is used to power photosynthesis.
   Cellular respiration still occurs to produce
   energy in plants.
5. Electrons (now low-energy) arrive at PS I ➞ photons
   from sunlight re-excite electrons to higher energy
   level
6. Electrons are passed to an electron acceptor and
   travel down another ETC
7. NADPH is formed by combining high energy
   electrons with NADP+
   a. NADPH transports high energy electrons to the
   Calvin cycle for glucose production

Question 12

Photolysis:

Answer 12

splitting of water by light that occurs in PS II.

Question 13

Cyclic Photophosphorylation

Answer 13

Steps: occurs in the stroma
lamellae; only involves PS I
1. Electrons in PS I get excited by sunlight to a high
energy state
2. Electrons get recycled passed back to the first ETC,
allowing more pumping of H+ and making more
ATP instead of NADPH (replenishes the ATP used in 3 phases of Calvin cycle

(1. Carbon fixation: taking carbon from an inorganic
source (CO2 in atmosphere) and converting it to an
organic compound (glucose)
a. Done by autotrophs (plants, photosynthetic
organisms, chemoautotrophic prokaryotes)
2. Reduction (steps that use up ATP and NADPH from
light reactions)
3. Regeneration: intermediates are regenerated so
cycle can continue)

Question 14

Important Steps of Calvin Cycle:

Answer 14

1. RuBisCo (most abundant enzyme on Earth)
   combines CO2 with RuBP, forming a 6 carbon
   intermediate (carbon fixation phase)
2. 6 carbon molecule is broken into two 3-carbon
   phosphoglycerate (PGA) molecules
3. PGA is phosphorylated to G3P (using ATP and
   NADPH during the reduction phase)
4. Most G3P is converted back to RuBP (requires ATP)
   and remaining G3P is used to make glucose
   (regeneration phase)
   a. 1 molecule of glucose is produced with 6 turns
   of the cycle (1 cycle produces 2 G3P molecules,
   so 6 cycles produce 12 G3P. 10 are used to
   reform RuBP, and the remaining 2 are used to
   make glucose)

Question 15

Photorespiration:

Answer 15

an undesirable process which reduces
the efficiency of carbon fixation, forming useless
byproducts. Occurs when RuBisCo binds O2 instead of CO2

Question 16

C2 (type of photosynthesis)

Answer 16

photorespiration; product = useless 2 carbon molecule
* Takes place in all plants
* Some plants have no way to stop C2 and
photosynthesize less efficiently

Question 17

C3: normal photosynthesis

Answer 17

• Takes place in all plants in the mesophyll cells

Question 18

C4:

Answer 18

prevents photorespiration by physically separating light
and dark reactions

Question 19

CAM:

Answer 19

minimizes water loss via temporal separation instead
of spatial (common in plants in dry environments e.g.
cactus)

Question 20

Stomata

Answer 20

pores found on bottom of leaves for gas
exchange. In most plants, stomata are always open for
continuous exchange of CO2 and O2, allowing water to
escape easily in certain environments

Question 21

what do CAM plants do differently

Answer 21

only open their stomata at night so that
CO2 can enter and less water is lost. However, there
is no sunlight at night, so there is no ATP/NADPH
from the light reactions to power the Calvin Cycle

Question 22

Cell division

Answer 22

how cells replicate to increase their number.

Question 23

Chromatin

Answer 23

a condensed form of DNA that is wrapped
around histones. DNA is stored as chromatin, but during
cell division, it condenses even more into chromosomes.

Question 24

Chromosomes:

Answer 24

dense packaging of chromatin, existing
during mitosis and meiosis. Chromosomes can be in
duplicated or unduplicated forms.

Question 25

Chromatid:

Answer 25

one half of a duplicated chromosome

Question 26

Sister Chromatids:

Answer 26

two duplicated chromatids that are completely identical to one another. They can connect at the centromere to form an X-shaped chromosome

Question 27

Centromere:

Answer 27

region where two sister chromatids are connected; kinetochores attach here

Question 28

n =

Answer 28

number of chromosomes in a set

Question 29

Haploid Human cells:

Answer 29

cells: n=23,

Question 30

Diploid Cells (2n)

Answer 30

have 2 sets of chromosomes: one from the mother and one from the father. The vast majority of human cells are diploid.

Question 31

Homologous Chromosomes

Answer 31

set of a chromosomes (one from each parent) in a pair. Found in diploid cells. Homologous chromosomes are similar in length, gene position, and centromere position. They carry genetic information for the same traits, but are not genetically identical.

Question 32

Centrosomes

Answer 32

the Microtubule Organizing Centers (MTOCs) of animal cells. A centrosome is composed of 2 centrioles perpendicular to each other.

Question 33

Spindle Fibers:

Answer 33

microtubules that emerge from the centrosome. They allow chromosomes and chromatids to be separated during specific phases of cell division.

Question 34

Mitosis:

Answer 34

nuclear division that creates a pair of diploid cells that are genetically identical to the original cell

Question 35

Mitosis Overview:

Answer 35

prophase → prometaphase → metaphase → anaphase → telophase and cytokinesis

Question 36

Prophase

Answer 36

* Chromatin condenses into chromosomes * Nucleolus disappears * Mitotic spindle begins to form * Centrosomes begin to move towards opposite ends of the cell

Question 37

Prometaphase

Answer 37

* Nucleus disassembles * Chromosomes condense even further * Each chromatid is attached to a kinetochore * Mitotic spindle further develops * Spindle fibers begin to attach to kinetochores of chromosomes

Question 38

Metaphase

Answer 38

* Chromosomes are lined up across the center of the cell (aka metaphase plate) * Centrosomes have reached opposite ends of the cell * Mitotic spindle is fully developed * All chromosomes are attached to spindle fibers via kinetochores

Question 39

Karyotyping

Answer 39

(physical observation of a cell’s chromosomes with a microscope)

Question 40

Anaphase

Answer 40

* Microtubules shorten * Sister chromatids are pulled apart - Once separated, each sister chromatid is now considered to be an individual chromosome

Question 41

Telophase

Answer 41

* Nucleoli redevelop * Two nuclear envelopes develop * Chromosomes decondense back into chromatin * Spindle fibers disappear * Cytokinesis occurs during telophase - Mitosis: the nucleus duplicates - Cytokinesis: the rest of the cell duplicates

Question 42

Cytokinesis:

Answer 42

physical division of the cytoplasm to form two cells.

Question 43

Animal cells form a

Answer 43

cleavage furrow (contractile ring formed by actin and myosin) forms; ring contracts to separating the dividing cells into two

Question 44

Plant cells form a

Answer 44

cell plate that develops between the two nuclei; essentially a cell wall that fuses with the existing plant cell wall, separating the two cells

Question 45

Meiosis:

Answer 45

nuclear division in that produces four haploid gametes that are not genetically identical to the original cell. Gametes are an organism’s reproductive cells (sperm in males, eggs in females).

Question 46

Cell Cycle:

Answer 46

an ordered sequence of events that occur before and during cell division.

Question 47

Interphase:

Answer 47

Interphase: when the cell is growing and preparing for cell division, but not actively dividing. Interphase ensures that each daughter cell will have enough biological material. Cells spend most of the cell cycle in interphase.

Question 48

The phases of interphase include:

Answer 48

G1, S, G2, G0, m phase

Question 49

G1 (Gap Phase 1):

Answer 49

cell grows in size and protein synthesis begins (preparation for cell division). ‣ Usually the longest phase of the cell cycle

Question 50

S (Synthesis Phase):

Answer 50

DNA and centrosomes are replicated. Sister chromatids are formed.

Question 51

G2 (Gap Phase 2):

Answer 51

final preparation for mitosis. Cell continues to grow, and organelles replicate. Cell checks that everything is ready (e.g. chromosomes are replicated) to proceed with mitosis.

Question 52

G0: resting phase.

Answer 52

Cells are active/functional, but are not dividing or preparing to divide

Question 53

Cells have to divide because of functional limitations:

Answer 53

SA to volume ratio, Genome to volume ratio

Question 54

checkpoints of cell cycle

Answer 54

End of G1:, end of G2, M Checkpoint/Spindle Checkpoint

Question 55

Density dependent inhibition:

Answer 55

cells stop dividing when the surrounding cell density reaches a maximum. Prevents overcrowded cells from dividing.

Question 56

Anchorage dependence:

Answer 56

cells will only divide when attached to an external surface a. Prevents cells from multiplying while floating freely through the body

Question 57

p53 gene:

Answer 57

an important tumor suppressor gene that regulates cell division * Mutation of p53 causes the cell to divide in an uncontrolled manner and leads to tumor formation