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AP® Biology
2003 Scoring Guidelines

The materials included in these files are intended for use by AP teachers
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These materials were produced by Educational Testing Service® (ETS®), which develops and administers the examinations of the Advanced Placement
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AP® BIOLOGY
2003 SCORING GUIDELINES
Question 1
In fruit flies, the phenotype for eye color is determined by a certain locus. E indicates the dominant allele
and e indicates the recessive allele. The cross between a male wild-type fruit fly and a female white-eyed fruit
fly produced the following offspring.
Wild-type
Male

White-eyed
Male

White-eyed
Female

Brown-eyed
Female

0

F1

Wild-type
Female
45

55

0

1

The wild-type and white-eyed individuals from the F1 generation were then crossed to produce the following
offspring.
F2

23

31

22

24

0

(a) Determine the genotypes of the original parents (P generation) and explain your reasoning. You may use
Punnett squares to enhance your description, but the results from the Punnett squares must be discussed in
your answer.
(b) Use a Chi-squared test on the F2 generation data to analyze your prediction of the parental genotypes.
Show all your work and explain the importance of your final answer.
(c) The brown-eyed female in the F1 generation resulted from a mutational change. Explain what a mutation
is, and discuss two types of mutations that might have produced the brown-eyed female in the F1
generation.
Critical Values of the Chi-Squared Distribution

Degrees of Freedom (df)

Probability (p)
1
3.84

0.05

2
5.99

3
7.82

4
9.49

5
11.1

The formula for Chi-squared is:
  (o-e)2 ¯
°
X2-œ ¡
¡¢ e °±

where o = observed number of individuals
e = expected number of individuals
å=

the sum of the values (in this case, the differences, squared, divided by the number expected)

Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

2
AP® BIOLOGY
2003 SCORING GUIDELINES
Question 1 (continued)
(a) Maximum 4 points
1 pt
1 pt
1 pt
1 pt
1 pt

Genotypes of the parents (words or symbols) XEY (or X+Y) and XeXe
Discuss/show how these resulted in this F1 (may be annotated Punnett)
Explain that it is a sex-linked (X-linked) gene (not just the word)
How you know which type is dominant
F2 results (may be annotated Punnett square)

(b) Maximum 4 points
1 pt
1 pt
1 pt
1 pt
1 pt

Correct F2 hypothesis (1:1:1:1; or 25/genotype)
Show work (components): o e o-e (o-e)2 (o-e)2/e
(or correct numbers (4/25 + 36/25 + 1/ 25 + 9/25 = 50/25 = 2; or at least the last term)
Sum: correct chi-square result ~ 2.0 or 1.85
degrees of freedom = 3 (critical value is 7.82)
correct interpretation of chi-square in terms of p
p = probability that the difference between the observed and the expected value is due to chance alone.
This p value shows we accept our hypothesis.
The null hypothesis is supported in this case.
(alternative: 2 Χ2 tests of white vs. red males and white vs. red females)

(c) Maximum 4 points
1 pt
Explain what a mutation is: (heritable) change in the DNA (code)
1-2 pts Discuss 2 types of mutations
May be: Point mutation, frameshift (deletion/duplication), insertion, transposition, break, inversion
within gene, base substitution, nonsense/stop, missense)
May NOT be: chromosomal aberration, nondisjunction, silent/neutral, transcription or translation or
processing error
1 pt
Molecular or biochemical elaboration beyond the explanation required

Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

3
AP® BIOLOGY
2003 SCORING GUIDELINES
Question 2
Regulatory (control) mechanisms in organisms are necessary for survival. Choose THREE of
the following examples and explain how each is regulated.
(i)

Flowering in plants

(ii) Water balance in plants
(iii)
(iv)

(i)

Water balance in terrestrial vertebrates
Body temperature in terrestrial vertebrates

Maximum 4 points

(each box represents an independent 1 point each)
long day (short night) plants
flower only if night is shorter
than a critical duration
change in
photocycle/photoperiod

- - - or - - short day (long night) plants
flower only if night exceeds a
critical duration

specific duration of
cold exposure
change in temperature pattern
(vernalization)

- - - or - - specified sequence of
temperature changes
initiate flowering

nutritional status

plant has enough nutritional
resources to support flowering

phytochromes
Pr Û Pfr
(night)
(day)
unknown “florigen” converts
shoot-meristem to floral-meristem
or breaks bud dormancy
leaf is photoreceptor organ
gibberellins ® ­flowering
auxins, ethylene, or abscisic acid®
¯flowering
can be independent of (day neutral) or
dependent on photocycle changes
unknown “florigen” transitions shoot
meristem to floral meristem
or break bud dormancy
gibberellins ® ­flowering
auxins, ethylene, or abscisic acid®
¯flowering
can be independent (day neutral) or codependent of photocycle changes
unknown “florigen” transitions shoot
meristem to floral meristem
or break bud dormancy
gibberellins ® ­flowering
auxins, ethylene, or abscisic acid®
¯flowering

Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

4
AP® BIOLOGY
2003 SCORING GUIDELINES
Question 2 (continued)
(ii) Maximum 4 points
Explain how the regulatory
mechanism affects water balance:
(2nd point must come from explanation
before 3rd point can be awarded)

Elaboration
(max 1 point)

- stomates/guard cells

closed » ¯water loss (evap/transpir)
open » ­water loss (evap/transpir)

ion, water influx/efflux from guard
cells; turgid/flaccid
(stomates: open/closed)

- altered stomate location
or “sunken stomates”
- cuticle thickening

stomates more abundant in more humid,
cooler regions of the plant
¯water loss (evap/transpir)

- increased succulence
- smaller leaves
- drop leaves
- altered leaf angle

water storage
¯water loss (evap/transpir)
¯water loss (evap/transpir)
¯water loss (evap/transpir)

- water potential in roots
lower than that of soil
- deeper root growth
- altered metabolic pattern
(e.g., CAM)
- increase cellular turgidity

permits water uptake, even in saline
soils
reach deeper water
stomates open only at night:
¯water loss (evap/transpir)
opposes osmotic force

Regulatory mechanism
(must earn one “explanation
point” before awarding a
second “mechanism point”)

waxy polymers resist water
movements, cutin

abscisic acid
less surface area directly exposed
to sun’s heat
production of organic osmolytes in
roots
cooler, more humid conditions
during the night
cell wall resists influx until
pressure gradient offsets osmotic
pressure

Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

5
AP® BIOLOGY
2003 SCORING GUIDELINES
Question 2 (continued)
(iii) Maximum 4 points
Hypothalamus is water-regulation center
(1 point max)
Regulatory mechanism/
detector/ signal
(must earn one “explanation
point” before awarding a
second “mechanism point”)
Hyperosmotic conditions result
in increased secretion of
Vasopressin (a.k.a. AntiDiuretic Hormone = ADH)
from the hypothalamus/
(posterior) pituitary (gland)
[[ hyposmotic opposite ]]
Hypovolemic conditions
activate RAAS system (renin
angiotensin activating
system), especially Ang II
from kidney/blood
Hypovolemic/ RAAS active
Ang II stimulates
hypothalamic thirst center
Hypovolemic/ RAAS active
Ang II stimulates secretion
of aldosterone from adrenal
(cortex) gland
Hypervolemic conditions
(excess blood volume) cause
increased secretion of Atrial
Natriuretic Peptide (ANP)
EVOLUTION
- loop of Henle
- type of nitrogenous waste
- development of specialized
transport epithelia, e.g., salt
glands
- cloaca development
- large intestine/ colon
- water-resistant body
surface
- behavioral avoidance of
dessicating conditions

Hypothalamus regulates neural circuits in
behavior of thirst
(1 point max)

Explain how the regulatory
mechanism affects water balance.
(2nd point must come from
explanation before 3rd point can be
awarded)

reduces water loss in urine

Elaboration
(1 point max)

­ water permeability in descending limb of
loop of Henle, distal tubule, or collecting
duct causes greater reabsorption of water
[[ hyposmotic opposite ]]

[[ hyposmotic opposite ]]
Ang II increases (Na+) and water
reabsorption in proximal tubule;
less urine

decreased renal blood pressure and filtrate
flow increase renin release; renin activates
angiotensinogen to Ang I, which is readily
converted to Ang II
juxtaglomerular apparatus (JGA)

Ang II increases thirst

“dry mouth” perception

Aldosterone increases (Na+) and
water reabsorption (& K+
secretion) in distal tubule
decreases (Na+) and water
reabsorption in distal tubule

inhibits renin and aldosterone release; causes
vasodilation of afferent arterioles

loop length a urine osmolarity
use less water in excretion

compare ammonia, urea, and uric acid
for water solubility or toxicity

less water loss in osmoregulation

use less water in excretion
greater surface area for water and
ion absorption
decrease water loss from body
surface
nocturnal habits reduce water loss
due to heat

Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

6
AP® BIOLOGY
2003 SCORING GUIDELINES
Question 2 (continued)
(iv) Maximum 4 points
Hypothalamus is thermostat
(1 point max)

1 Regulatory mechanism
(must earn one “explanation
point” before awarding a
second “mechanism point”)
- move to a location that is:
cooler if hot (e.g., shade), or
warmer if cold (e.g., bask)
- sweat/ perspire when hot
- lick body surface when hot
- pant when hot
- alter insulation (fur, feathers):
flat when hot . . . . . . . . . . . .
or erect when cold . . . . . . . . . .
- ­ peripheral:
vasodilation when hot, or
vasoconstriction when cold
- ­shivering when cold
- ­non-shivering thermogenesis
when cold
- ­activity when cold
- activate heat-shock
proteins when hot
- torpor
estivate when hot . . . . . . . .
or
hibernate when cold . . . . . .
- ­ surface area (e.g., big ears)
- ¯ surface area
- ¯body fat
- shed insulation when hot
- grow insulation when cold
- ­metabolic rate when cold
- ¯metabolic rate when hot
- ¯surface area:volume
- counter-current heat
exchange/blood flow

Thermostat reset by different
conditions; autonomic/other neural
outputs influence body temperature
(1 point max)
Explain how the regulatory
mechanism affects temperature
regulation. (2nd point must come
from explanation before 3rd point
can be awarded)

Fever, hypothermia
(1 point max)

Elaboration
(1 point max)

­heat loss from body
¯heat loss from body
­ evaporative cooling
­evaporative cooling
­evaporative cooling
­heat loss
¯heat loss

¯boundary layer
­boundary layer

blood at periphery to ­heat loss
blood kept in core of body
­heat production
­heat production

contraction/relaxation cycling in
skeletal muscles
metabolism of brown fat

­metabolic heat production
intracelluar protection of protein
structure

HSPs are chaperones that guide protein
folding

¯ activity & ¯ metabolism ®
¯ metabolic heat

sometimes triggered by changes in day
length

¯activity and slower metabolism ¯
heat loss during cold winter
­heat loss
¯heat loss
­heat loss
­heat loss
¯heat loss
­heat production
¯heat production
¯heat loss
¯heat loss by keeping core
warmer than periphery

sometimes triggered by changes in day
length

­boundary layer
­thyroid hormones
¯thyroid hormones
heat transferred from arterial to venous
vessels

Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

7
AP® BIOLOGY
2003 SCORING GUIDELINES
Question 3
Many populations exhibit the following growth curve:

(a) Describe what is occurring in the population during phase A.
(b) Discuss THREE factors that might cause the fluctuations shown in phase B.
(c) Organisms demonstrate exponential (r) or logistic (K) reproductive strategies. Explain these two
strategies and discuss how they affect population size over time.
**Global point; 1 point: Carrying capacity definition: The number of individuals of a particular species that an
environment can support; determined by the availability of resources. Point can be earned in any section.
(a) Maximum 3 points
1 point for each part of curve
#3

population growth slows as population
approaches the carrying capacity; deceleration.
No point for stating that population reaches
carrying capacity — must indicate rate change
(slows) or levels off.

#2

exponential growth; log phase; period of rapid
growth; dramatically or rapidly increasing

3

2

1

#1 establishment period or lag phase: population
grows slowly or does not grow. No credit for
small population size, must indicate slow growth
rate

Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

8
AP® BIOLOGY
2003 SCORING GUIDELINES
Question 3 (continued)

(b) Maximum 4 points
3 points: Three biologically sound factors that discuss the rise or fall of population size. Only the first three
factors discussed will be scored. Commonly used density-dependent factors include limited resources,
predation (predator/prey cycles), disease, and reproduction. Density-independent factors must reflect the
periodic nature of the curve and cannot include cataclysmic events such as earthquakes, volcanoes, etc.
For each example to be legitimate, it must
· have a biologically sound explanation/discussion
· have a cause and an effect
· fit the graph in phase B
1 point for explanation of a complete cycle (rise and fall of population size.)
(c) Maximum 4 points
Explanation: 2 points (1 each for r and for K) Each explanation must have at least two characteristics from
the table
r-strategists
Many young
Little energy investment in each
Small young
Rapid sexual maturation
Higher incidence of asexual reproduction
Brief reproductive life span
Little or no parental care
“Big bang” (semelparous) reproduction
Unpredictable environment
Population control by density-independent
factors
Short life span
Type III survivorship curve; few offspring
survive
Not prone to extinction
Higher reproductive capacity

K-strategists
Few young
High energy investment in each
Large young
Slow sexual maturation
Higher incidence of sexual reproduction
Long reproductive life span
Lots of parental care
Many reproductive events (iteroparous)
Predictable environment
Population control by density-dependent factors
Long life span
Type I survivorship curve; many offspring
survive
Prone to extinction
Lower reproductive capacity

Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

9
AP® BIOLOGY
2003 SCORING GUIDELINES
Question 3 (continued)
Discussion: 2 points (1 point each) Note: No points for a graph without an explanation

boom/bust (great fluctuations) in population size

population stabilizes around K (carrying capacity)

Population Size

K-strategists

Population Size

r-strategists

Time

Time

Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

10
AP® BIOLOGY
2003 SCORING GUIDELINES
Question 4
Death is a natural and necessary part of life cycles at all levels of organization.
(a) Discuss TWO examples of how cell death affects the development and functioning of a
multicellular organism.
(b) Discuss ONE example of how substances are degraded and reused in cells.
(c) Discuss the evolutionary significance of death.
(a) Maximum 6 points (3 points per example)
·
·
·

1 pt. Example of cell death leading to a change in development
1 pt. Example of cell death leading to a change in function
1 pt. Discussion of how cell death occurs or an extension of cell death significance
Examples (categories) of cell death
· elimination of cells, tissues, and organs
· tissue remodeling / reconstruction
· destruction that poses a threat to the survival of the organism
· repair / maintenance
· cell death as a result of severe injury
· cell death as a result of exposure to toxins / altered chemical balance
· cell death as a result of aging

(b) Maximum 3 points
1 pt. Substance: how degraded to product
1 pt. Product: how reused in cells
1 pt. Discussion / elaboration on process to degrade or reuse
* “Energy” is not a substance in this response.
(c) Maximum 3 points
Relate evolution to death:
- change in allele or phenotype frequency / removal of individuals from a population based on
phenotype / differential reproduction
- selection based on variation
- competition (struggle, resource availability, overpopulation) having an effect on reproductive
success
- speciation / mass extinction / adaptive radiation
- genetic drift
- cell death genes preserved early in evolution
- mechanism of apoptosis (changes that occur within the cell)
- activation / inhibition of cell death genes
- effect on embryonic development
Copyright © 2003 by College Entrance Examination Board. All rights reserved.
Available at apcentral.collegeboard.com.

11

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Ap03 sg biology_26426

  • 1. AP® Biology 2003 Scoring Guidelines The materials included in these files are intended for use by AP teachers for course and exam preparation; permission for any other use must be sought from the Advanced Placement Program®. Teachers may reproduce them, in whole or in part, in limited quantities for noncommercial, face-to-face teaching purposes. This permission does not apply to any third-party copyrights contained herein. This material may not be mass distributed, electronically or otherwise. These materials and any copies made of them may not be resold, and the copyright notices must be retained as they appear here. These materials were produced by Educational Testing Service® (ETS®), which develops and administers the examinations of the Advanced Placement Program for the College Board. The College Board and Educational Testing Service (ETS) are dedicated to the principle of equal opportunity, and their programs, services, and employment policies are guided by that principle. The College Board is a national nonprofit membership association whose mission is to prepare, inspire, and connect students to college and opportunity. Founded in 1900, the association is composed of more than 4,300 schools, colleges, universities, and other educational organizations. Each year, the College Board serves over three million students and their parents, 22,000 high schools, and 3,500 colleges through major programs and services in college admissions, guidance, assessment, financial aid, enrollment, and teaching and learning. Among its best-known programs are the SAT®, the PSAT/NMSQT®, and the Advanced Placement Program® (AP®). The College Board is committed to the principles of equity and excellence, and that commitment is embodied in all of its programs, services, activities, and concerns. For further information, visit www.collegeboard.com Copyright © 2003 College Entrance Examination Board. All rights reserved. College Board, Advanced Placement Program, AP, AP Vertical Teams, APCD, Pacesetter, Pre-AP, SAT, Student Search Service, and the acorn logo are registered trademarks of the College Entrance Examination Board. AP Central is a trademark owned by the College Entrance Examination Board. PSAT/NMSQT is a registered trademark jointly owned by the College Entrance Examination Board and the National Merit Scholarship Corporation. Educational Testing Service and ETS are registered trademarks of Educational Testing Service. Other products and services may be trademarks of their respective owners. For the College Board’s online home for AP professionals, visit AP Central at apcentral.collegeboard.com.
  • 2. AP® BIOLOGY 2003 SCORING GUIDELINES Question 1 In fruit flies, the phenotype for eye color is determined by a certain locus. E indicates the dominant allele and e indicates the recessive allele. The cross between a male wild-type fruit fly and a female white-eyed fruit fly produced the following offspring. Wild-type Male White-eyed Male White-eyed Female Brown-eyed Female 0 F1 Wild-type Female 45 55 0 1 The wild-type and white-eyed individuals from the F1 generation were then crossed to produce the following offspring. F2 23 31 22 24 0 (a) Determine the genotypes of the original parents (P generation) and explain your reasoning. You may use Punnett squares to enhance your description, but the results from the Punnett squares must be discussed in your answer. (b) Use a Chi-squared test on the F2 generation data to analyze your prediction of the parental genotypes. Show all your work and explain the importance of your final answer. (c) The brown-eyed female in the F1 generation resulted from a mutational change. Explain what a mutation is, and discuss two types of mutations that might have produced the brown-eyed female in the F1 generation. Critical Values of the Chi-Squared Distribution Degrees of Freedom (df) Probability (p) 1 3.84 0.05 2 5.99 3 7.82 4 9.49 5 11.1 The formula for Chi-squared is:   (o-e)2 ¯ ° X2-œ ¡ ¡¢ e °± where o = observed number of individuals e = expected number of individuals å= the sum of the values (in this case, the differences, squared, divided by the number expected) Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 2
  • 3. AP® BIOLOGY 2003 SCORING GUIDELINES Question 1 (continued) (a) Maximum 4 points 1 pt 1 pt 1 pt 1 pt 1 pt Genotypes of the parents (words or symbols) XEY (or X+Y) and XeXe Discuss/show how these resulted in this F1 (may be annotated Punnett) Explain that it is a sex-linked (X-linked) gene (not just the word) How you know which type is dominant F2 results (may be annotated Punnett square) (b) Maximum 4 points 1 pt 1 pt 1 pt 1 pt 1 pt Correct F2 hypothesis (1:1:1:1; or 25/genotype) Show work (components): o e o-e (o-e)2 (o-e)2/e (or correct numbers (4/25 + 36/25 + 1/ 25 + 9/25 = 50/25 = 2; or at least the last term) Sum: correct chi-square result ~ 2.0 or 1.85 degrees of freedom = 3 (critical value is 7.82) correct interpretation of chi-square in terms of p p = probability that the difference between the observed and the expected value is due to chance alone. This p value shows we accept our hypothesis. The null hypothesis is supported in this case. (alternative: 2 Χ2 tests of white vs. red males and white vs. red females) (c) Maximum 4 points 1 pt Explain what a mutation is: (heritable) change in the DNA (code) 1-2 pts Discuss 2 types of mutations May be: Point mutation, frameshift (deletion/duplication), insertion, transposition, break, inversion within gene, base substitution, nonsense/stop, missense) May NOT be: chromosomal aberration, nondisjunction, silent/neutral, transcription or translation or processing error 1 pt Molecular or biochemical elaboration beyond the explanation required Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 3
  • 4. AP® BIOLOGY 2003 SCORING GUIDELINES Question 2 Regulatory (control) mechanisms in organisms are necessary for survival. Choose THREE of the following examples and explain how each is regulated. (i) Flowering in plants (ii) Water balance in plants (iii) (iv) (i) Water balance in terrestrial vertebrates Body temperature in terrestrial vertebrates Maximum 4 points (each box represents an independent 1 point each) long day (short night) plants flower only if night is shorter than a critical duration change in photocycle/photoperiod - - - or - - short day (long night) plants flower only if night exceeds a critical duration specific duration of cold exposure change in temperature pattern (vernalization) - - - or - - specified sequence of temperature changes initiate flowering nutritional status plant has enough nutritional resources to support flowering phytochromes Pr Û Pfr (night) (day) unknown “florigen” converts shoot-meristem to floral-meristem or breaks bud dormancy leaf is photoreceptor organ gibberellins ® ­flowering auxins, ethylene, or abscisic acid® ¯flowering can be independent of (day neutral) or dependent on photocycle changes unknown “florigen” transitions shoot meristem to floral meristem or break bud dormancy gibberellins ® ­flowering auxins, ethylene, or abscisic acid® ¯flowering can be independent (day neutral) or codependent of photocycle changes unknown “florigen” transitions shoot meristem to floral meristem or break bud dormancy gibberellins ® ­flowering auxins, ethylene, or abscisic acid® ¯flowering Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 4
  • 5. AP® BIOLOGY 2003 SCORING GUIDELINES Question 2 (continued) (ii) Maximum 4 points Explain how the regulatory mechanism affects water balance: (2nd point must come from explanation before 3rd point can be awarded) Elaboration (max 1 point) - stomates/guard cells closed » ¯water loss (evap/transpir) open » ­water loss (evap/transpir) ion, water influx/efflux from guard cells; turgid/flaccid (stomates: open/closed) - altered stomate location or “sunken stomates” - cuticle thickening stomates more abundant in more humid, cooler regions of the plant ¯water loss (evap/transpir) - increased succulence - smaller leaves - drop leaves - altered leaf angle water storage ¯water loss (evap/transpir) ¯water loss (evap/transpir) ¯water loss (evap/transpir) - water potential in roots lower than that of soil - deeper root growth - altered metabolic pattern (e.g., CAM) - increase cellular turgidity permits water uptake, even in saline soils reach deeper water stomates open only at night: ¯water loss (evap/transpir) opposes osmotic force Regulatory mechanism (must earn one “explanation point” before awarding a second “mechanism point”) waxy polymers resist water movements, cutin abscisic acid less surface area directly exposed to sun’s heat production of organic osmolytes in roots cooler, more humid conditions during the night cell wall resists influx until pressure gradient offsets osmotic pressure Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 5
  • 6. AP® BIOLOGY 2003 SCORING GUIDELINES Question 2 (continued) (iii) Maximum 4 points Hypothalamus is water-regulation center (1 point max) Regulatory mechanism/ detector/ signal (must earn one “explanation point” before awarding a second “mechanism point”) Hyperosmotic conditions result in increased secretion of Vasopressin (a.k.a. AntiDiuretic Hormone = ADH) from the hypothalamus/ (posterior) pituitary (gland) [[ hyposmotic opposite ]] Hypovolemic conditions activate RAAS system (renin angiotensin activating system), especially Ang II from kidney/blood Hypovolemic/ RAAS active Ang II stimulates hypothalamic thirst center Hypovolemic/ RAAS active Ang II stimulates secretion of aldosterone from adrenal (cortex) gland Hypervolemic conditions (excess blood volume) cause increased secretion of Atrial Natriuretic Peptide (ANP) EVOLUTION - loop of Henle - type of nitrogenous waste - development of specialized transport epithelia, e.g., salt glands - cloaca development - large intestine/ colon - water-resistant body surface - behavioral avoidance of dessicating conditions Hypothalamus regulates neural circuits in behavior of thirst (1 point max) Explain how the regulatory mechanism affects water balance. (2nd point must come from explanation before 3rd point can be awarded) reduces water loss in urine Elaboration (1 point max) ­ water permeability in descending limb of loop of Henle, distal tubule, or collecting duct causes greater reabsorption of water [[ hyposmotic opposite ]] [[ hyposmotic opposite ]] Ang II increases (Na+) and water reabsorption in proximal tubule; less urine decreased renal blood pressure and filtrate flow increase renin release; renin activates angiotensinogen to Ang I, which is readily converted to Ang II juxtaglomerular apparatus (JGA) Ang II increases thirst “dry mouth” perception Aldosterone increases (Na+) and water reabsorption (& K+ secretion) in distal tubule decreases (Na+) and water reabsorption in distal tubule inhibits renin and aldosterone release; causes vasodilation of afferent arterioles loop length a urine osmolarity use less water in excretion compare ammonia, urea, and uric acid for water solubility or toxicity less water loss in osmoregulation use less water in excretion greater surface area for water and ion absorption decrease water loss from body surface nocturnal habits reduce water loss due to heat Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 6
  • 7. AP® BIOLOGY 2003 SCORING GUIDELINES Question 2 (continued) (iv) Maximum 4 points Hypothalamus is thermostat (1 point max) 1 Regulatory mechanism (must earn one “explanation point” before awarding a second “mechanism point”) - move to a location that is: cooler if hot (e.g., shade), or warmer if cold (e.g., bask) - sweat/ perspire when hot - lick body surface when hot - pant when hot - alter insulation (fur, feathers): flat when hot . . . . . . . . . . . . or erect when cold . . . . . . . . . . - ­ peripheral: vasodilation when hot, or vasoconstriction when cold - ­shivering when cold - ­non-shivering thermogenesis when cold - ­activity when cold - activate heat-shock proteins when hot - torpor estivate when hot . . . . . . . . or hibernate when cold . . . . . . - ­ surface area (e.g., big ears) - ¯ surface area - ¯body fat - shed insulation when hot - grow insulation when cold - ­metabolic rate when cold - ¯metabolic rate when hot - ¯surface area:volume - counter-current heat exchange/blood flow Thermostat reset by different conditions; autonomic/other neural outputs influence body temperature (1 point max) Explain how the regulatory mechanism affects temperature regulation. (2nd point must come from explanation before 3rd point can be awarded) Fever, hypothermia (1 point max) Elaboration (1 point max) ­heat loss from body ¯heat loss from body ­ evaporative cooling ­evaporative cooling ­evaporative cooling ­heat loss ¯heat loss ¯boundary layer ­boundary layer blood at periphery to ­heat loss blood kept in core of body ­heat production ­heat production contraction/relaxation cycling in skeletal muscles metabolism of brown fat ­metabolic heat production intracelluar protection of protein structure HSPs are chaperones that guide protein folding ¯ activity & ¯ metabolism ® ¯ metabolic heat sometimes triggered by changes in day length ¯activity and slower metabolism ¯ heat loss during cold winter ­heat loss ¯heat loss ­heat loss ­heat loss ¯heat loss ­heat production ¯heat production ¯heat loss ¯heat loss by keeping core warmer than periphery sometimes triggered by changes in day length ­boundary layer ­thyroid hormones ¯thyroid hormones heat transferred from arterial to venous vessels Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 7
  • 8. AP® BIOLOGY 2003 SCORING GUIDELINES Question 3 Many populations exhibit the following growth curve: (a) Describe what is occurring in the population during phase A. (b) Discuss THREE factors that might cause the fluctuations shown in phase B. (c) Organisms demonstrate exponential (r) or logistic (K) reproductive strategies. Explain these two strategies and discuss how they affect population size over time. **Global point; 1 point: Carrying capacity definition: The number of individuals of a particular species that an environment can support; determined by the availability of resources. Point can be earned in any section. (a) Maximum 3 points 1 point for each part of curve #3 population growth slows as population approaches the carrying capacity; deceleration. No point for stating that population reaches carrying capacity — must indicate rate change (slows) or levels off. #2 exponential growth; log phase; period of rapid growth; dramatically or rapidly increasing 3 2 1 #1 establishment period or lag phase: population grows slowly or does not grow. No credit for small population size, must indicate slow growth rate Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 8
  • 9. AP® BIOLOGY 2003 SCORING GUIDELINES Question 3 (continued) (b) Maximum 4 points 3 points: Three biologically sound factors that discuss the rise or fall of population size. Only the first three factors discussed will be scored. Commonly used density-dependent factors include limited resources, predation (predator/prey cycles), disease, and reproduction. Density-independent factors must reflect the periodic nature of the curve and cannot include cataclysmic events such as earthquakes, volcanoes, etc. For each example to be legitimate, it must · have a biologically sound explanation/discussion · have a cause and an effect · fit the graph in phase B 1 point for explanation of a complete cycle (rise and fall of population size.) (c) Maximum 4 points Explanation: 2 points (1 each for r and for K) Each explanation must have at least two characteristics from the table r-strategists Many young Little energy investment in each Small young Rapid sexual maturation Higher incidence of asexual reproduction Brief reproductive life span Little or no parental care “Big bang” (semelparous) reproduction Unpredictable environment Population control by density-independent factors Short life span Type III survivorship curve; few offspring survive Not prone to extinction Higher reproductive capacity K-strategists Few young High energy investment in each Large young Slow sexual maturation Higher incidence of sexual reproduction Long reproductive life span Lots of parental care Many reproductive events (iteroparous) Predictable environment Population control by density-dependent factors Long life span Type I survivorship curve; many offspring survive Prone to extinction Lower reproductive capacity Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 9
  • 10. AP® BIOLOGY 2003 SCORING GUIDELINES Question 3 (continued) Discussion: 2 points (1 point each) Note: No points for a graph without an explanation boom/bust (great fluctuations) in population size population stabilizes around K (carrying capacity) Population Size K-strategists Population Size r-strategists Time Time Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 10
  • 11. AP® BIOLOGY 2003 SCORING GUIDELINES Question 4 Death is a natural and necessary part of life cycles at all levels of organization. (a) Discuss TWO examples of how cell death affects the development and functioning of a multicellular organism. (b) Discuss ONE example of how substances are degraded and reused in cells. (c) Discuss the evolutionary significance of death. (a) Maximum 6 points (3 points per example) · · · 1 pt. Example of cell death leading to a change in development 1 pt. Example of cell death leading to a change in function 1 pt. Discussion of how cell death occurs or an extension of cell death significance Examples (categories) of cell death · elimination of cells, tissues, and organs · tissue remodeling / reconstruction · destruction that poses a threat to the survival of the organism · repair / maintenance · cell death as a result of severe injury · cell death as a result of exposure to toxins / altered chemical balance · cell death as a result of aging (b) Maximum 3 points 1 pt. Substance: how degraded to product 1 pt. Product: how reused in cells 1 pt. Discussion / elaboration on process to degrade or reuse * “Energy” is not a substance in this response. (c) Maximum 3 points Relate evolution to death: - change in allele or phenotype frequency / removal of individuals from a population based on phenotype / differential reproduction - selection based on variation - competition (struggle, resource availability, overpopulation) having an effect on reproductive success - speciation / mass extinction / adaptive radiation - genetic drift - cell death genes preserved early in evolution - mechanism of apoptosis (changes that occur within the cell) - activation / inhibition of cell death genes - effect on embryonic development Copyright © 2003 by College Entrance Examination Board. All rights reserved. Available at apcentral.collegeboard.com. 11