IB DP Biology Topic 9: Plant biology :9.4 Reproduction in plants-HL Paper 2


The drawing shows a flower of red valerian, Centranthus ruber.

(a) State the name and function of structures I and II.
Structure I name and function: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Structure II name and function: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) Structure III is the ovary. Outline the processes that occur in the ovary.

(c) Structure IV contains a gland that secretes a sugary liquid. Suggest a benefit to the plant of secreting this liquid.



a. I is the stigma which receives the pollen/where pollen lands/is captured (during pollination);
b. II is the anther and produces/contains/releases pollen;

a. female gamete/ovule is produced/meiosis to produce ovules/ovule develops;
b. Fertilisation occurs
fusion/union of male and female gametes/nuclei;
c. development of seed (from fertilised ovule);
d. development of fruit (from the whole ovary);

a. attracts an insect/animal/which pollinates the flower;
b. attracts a pollinator;


(a) The images show parts of plants belonging to two different phyla.

Plant X                                                                                                                                        Plant Y


State the phylum of plant X and of plant Y. [2]



(b) Some plant families, such as the figwort family, have been reclassified on the basis of evidence from cladistics. Explain the methods that have been used recently to reclassify groups of plants. [3]

(c) Successful sexual reproduction in flowering plants depends on several essential processes. Outline the role of pollination and seed dispersal. [2]


Seed dispersal:



a X: Filicinophyta  2 Y: Coniferophyta/Conifera/Gymnosperms 


a. «previous» classification used to be based on the appearance/structures of the plant/leaves/flowers/seeds/analogy/phenotype 

b. «modern cladistics uses» RNA/DNA nucleotide/base sequencing/amino acid sequencing/homology

c. DNA mutation occurs at a relatively constant rate allowing estimation of when species

d. a shared/common derived characteristic places organisms in the same clade 

e. the number of changes in sequences indicates distance from common ancestor OR the fewer the differences «in sequences» means the closer the relationship 


transfer/dispersal/movement of pollen from anther/stamen to stigma
transfer/dispersal/movement of pollen between plants/flowers prior to/allowing
fertilization ✔
seed dispersal:
«strategy of» distribution of seeds so that new plants have space/nutrients to
develop/avoid competition/colonize new habitats ✔


Draw a half-view of an animal-pollinated flower. [4]



a sepals as outermost part of flower  

b petals as largest part of flower 


stamen drawn with recognizable anther and filament
anther and filament shown as parts of the stamen ✔


carpel/pistil drawn with recognizable stigma, style and ovary
stigma, style and ovary shown as parts of the carpel ✔

e nectary at base of the ovary 

f ovule inside the ovary  

As the question does not specify a labelled half- view, allow some marks for unlabeled structures: award one mark for any two of the six structures in the mark scheme (mpa to mpf). It must be clear what each unlabeled part is. The maximum mark is therefore 3 for an unlabeled half-view. 


Plants have widespread influences, from food chains to climate change.

Draw a labelled diagram of the internal structure of a seed.


Plants have widespread influences, from food chains to climate change.

Explain the process of water uptake and transport by plants.



a. radicle/embryo root shown tapering to a root tip

b. plumule/embryo shoot shown with embryonic leaves «in a dicot seed» drawn and labelled


    plumule/embryo shoot shown tapering to a shoot tip «in a monocot seed»

c. seed coat/testa shown with a double line

d. cotyledon/endosperm shown as a large structure «for food storage»

e. embryo shown with both embryo root and shoot visible

Accept any dicot or monocot seed


Award [1] for any of the structure clearly drawn and labelled

Award mpe only if mpa and mpb have not been awarded and the labelling line points clearly to the plumule or radicle or both.

[Max 3 Marks]


a. roots/root hairs absorb water

b. water is absorbed by osmosis

c. solute concentration inside the root is higher/water potential is lower «than in the soil»

d. due to active transport of ions/minerals into the root

e. transport of water in xylem vessels

f. flow/stream of water from roots to leaves

g. water movement in xylem due to pulling force/transpiration pull/suction/negative pressure potential

h. cohesion/hydrogen bonds between water molecules «allows water to be pulled up in xylem»

i. transpiration in leaves generates tension/pulling forces/suction

j. evaporation of water from «leaf» cell walls

k. adhesion of water to «leaf» cell walls/cellulose creates tension «forces»

Not adhesion to xylem walls in mpk and the adhesion must be linked to creating tension

l. lignin in xylem walls/thickened xylem walls prevent collapse/resist tension

m. «movement of water in xylem is a» passive process

[Max 8 Marks]



Angiospermophyta are vascular flowering plants. 

Describe the transport of organic compounds in vascular plants.


The flowers of angiospermophyta are used for sexual reproduction. Outline three processes required for successful reproduction of angiospermophyta.


Growth in living organisms includes replication of DNA. Explain DNA replication.



a. phloem transports organic compounds/sucrose

b. from sources/leaves/where produced to sinks/roots/where used

c. through sieve tubes/columns of cells with sieve plates/perforated end walls

d. loading of organic compounds/sucrose into /H+ ions out of phloem/sieve tubes by active transport/using ATP

e. high solute concentration causes water to enter by osmosis (at source)

f. high (hydrostatic) pressure causes flow (from source to sink)

g. companion cells help with loading / plasmodesmata provide a path between sieve tubes and companion cell

h. translocation/mass flow


a. meiosis / production of male and female gametes

b. pollination / transfer of pollen from anther to stigma

c. fertilization happens after pollination / fertilisation is joining of gametes

d. seed dispersal / spread of seeds to new locations

Reject fruit dispersal.


a. helicase unwinds the double helix

b. gyrase/topoisomerase relieves strains during uncoiling

c. helicase separates the two strands of DNA/breaks hydrogen bonds

Accept unzips here but not for mark point a.

d. each single strand acts as a template for a new strand / process is semi-conservative

e. DNA polymerase III can only add nucleotides to the end of an existing chain/to a primer 

f. (DNA) primase adds RNA primer/short length of RNA nucleotides

g. DNA polymerase (III) adds nucleotides in a 5’ to 3’ direction

h. complementary base pairing / adenine to thymine and cytosine to guanine

Do not accept letters.

i. DNA polymerase (III) moves towards the replication fork on one strand and away from it on the other strand

j. continuous on the leading strand and discontinuous/fragments formed on the lagging strand

k. DNA polymerase I replaces primers/RNA with DNA

l. ligase joins the fragments together/seals the nicks



Explain how minerals move into plants.


Outline the conditions needed for the germination of a typical seed.


Following germination of seeds, plants undergo a rapid increase in the number of cells. Describe stages in the cell cycle that result in this increase of cells.



Remember, up to TWO “quality of construction” marks per essay.

a. minerals bound to soil particles;
b. examples of three nutrients from: phosphate, nitrate, magnesium, iron, calcium, potassium, sodium, magnesium;
c. minerals dissolve in water;
d. mass flow causes movement of minerals with movement of water through soil;
e. minerals diffuse down a concentration gradient towards roots (as the mineral concentration next to the roots is continuously decreasing);
f. minerals enter the plant through roots;
g. by active transport / use of ATP;
h. branching of roots increases surface area for absorption of minerals;
i. root hairs increase surface area (for the absorption of minerals);
j. hypha of (mutualistic) fungi may enhance movement of selected ions into roots / increase surface area;
k. root hairs have many mitochondria to provide energy/ATP for active transport;
l. export of H+ creates electrochemical gradient / displaces ions bound to soil/clay;
m. that causes positive mineral ions to diffuse into (root) cells;
n. negative mineral ions cross membrane linked to H+ ions moving down (H+) gradient;


Remember, up to TWO “quality of construction” marks per essay.

a. water to rehydrate the seed / activate metabolic processes;
b. oxygen for aerobic respiration as seed germinates;
c. suitable temperature for enzyme activity;
d. each type of seed has specific temperature requirements / temperature requirements ensure that seeds germinate at the correct time of year;
Do not accept a simple list of factors without details.


Remember, up to TWO “quality of construction” marks per essay.

a. growth phase/G-1: synthesis of proteins/cytoplasm/organelles;
b. synthesis phase/S-phase: replication of DNA;
c. second growth phase/G-2: continued growth of cytoplasm/molecular synthesis/duplication of organelles;
d. prophase: chromosomes super-coil to prepare for mitosis / nuclear envelope disappears / spindle fibres form;
e. metaphase: chromosomes line up at equatorial/metaphase plate / spindle fibres attach to centromeres/chromosomes;
f. anaphase: chromatids move along microtubules/spindle fibres move chromatids toward opposite poles;
g. telophase: nuclear membranes form around each cluster of chromosomes;
h. cytokinesis: new plasma membrane forms between the nuclei / cell plate forms;
i. a new cell wall forms;
j. (mitosis) results in two cells with identical nuclei;

Names of phases are required to earn the mark.
Award marks for a clearly drawn correctly annotated diagram.

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