Unit 4.2 - Sexual reproduction in plants Flashcards
(236 cards)
1
Q
What make up the carpel in an insect pollinated flower?
A
Stigma
Style
Ovary
2
Q
What do the stigma, style and ovary make up in an insect pollinated flower?
A
The carpel
3
Q
Carpel
A
Inner structure of flower
4
Q
What make up the stamen of an insect pollinated flower?
A
Anther
Filament
5
Q
What do the anther and filament make up in an insect pollinated flower?
A
The stamen
6
Q
What does pollen do?
A
Carries male gametes
7
Q
Pollination
A
The transfer of pollen from one flower to another (or within the same flower)
8
Q
Describe the petals of insect pollinated flowers
A
Are large and colourful in order to attract insects
9
Q
Describe the sepal of insect pollinated flowers
A
Forms the bud within the early stages of development and protects the flower within whilst its developing
10
Q
What form the bud during the early stages of development of a flower?
A
The sepal
11
Q
Describe the receptacle of insect pollinated flowers
A
Where the whole flower structure is attached
12
Q
Describe the pedicel of insect pollinated flowers
A
Holds the flower up
13
Q
Describe the ovary of insect pollinated flowers
A
Has several ovules, which is where female gametes develop
14
Q
Where do female gametes develop in flowers?
A
In ovules in the ovaries
15
Q
Describe the nectary of insect pollinated flowers
A
Where nectar is produced - a sweet, sugary fluid that insects feed on
16
Q
Explain the mutualistic relationship between plants and insects?
A
When insects go to collet nectar from the nectary, they brush past the anther when collecting this
They transfer pollen to the stigma, which is sticky = pollination
17
Q
What do insects carry from flower to flower?
A
Pollen
18
Q
How does the stigma get the pollen from insects?
A
It’s sticky
19
Q
How do pollinating insects benefit from the process of pollination?
A
The flowers provide nectar as a reward
20
Q
What features can wind pollinated flowers have?
A
Fast growing
High productivity
21
Q
What are the things to label on a wind-pollinated flower?
A
Bract
Stigma
Anther
Ovary
22
Q
What does the anther in wind pollinated flowers do?
A
Releases pollen into the air
23
Q
What does the bract in wind pollinated flowers do?
A
Is protective
24
Q
Which part of a wind pollinated flower is adapted for its function? Describe this
A
Stigma
Is feathery to increase its surface area so that it’s more likely to catch pollen grains
25
What does the ovary in wind pollinated flowers do?
Contains the ovules
26
Why do wind pollinated flowers not have petals?
No need to attract insects
27
What adaptation do wind pollinated flowers have to obtain pollen blown in the wind? Explain this
High up off he ground on a stalk to catch the wind current and catch the pollen blown in the wind
28
Summarise the things we can compare between wind and insect-pollinated flowers
Petals
Stigma
Anthers
Pollen grains
29
Compare the petals of a wind-pollinated flower to an insect-pollinated flower
Petals small and green or no petals at all. The flowers are located above the leaves or produced in early spring to give maximum advantage from wind currents without interference from leaves.
V.s
Large and brightly coloured petals, often with guidelines to the nectaries to attract the insect pollinators
30
Compare the stigma of a wind-pollinated flower to an insect-pollinated flower
The stigmas are large and feathery and hang outside the flower to catch airborne pollen in wind currents
V.s
The stigma is sticky to trap pollen grains and is inside the flower, where insects rub against it thus causing pollen to be deposited
31
Compare the anther of a wind-pollinated flower to an insect-pollinated flower
Large anthers suspended outside the flower to release pollen grains into wind currents
V.s
Anthers on rigid filaments inside the flower: where insects must rub against them. This increases the change of pollen being deposited on insects’ bodies
32
Compare the pollen grains of wind-pollinated flowers to an insect-pollinated flowers
Vast numbers of small, light, smooth-walled pollen grains are produced which are easily carried by the wind
V.s
The pollen grains are large with spiky and sculptured walls which stick to insect bodies
33
Describe and explain the guidelines on the petals of insect-pollinated flowers
These lines show up brightly in UV light
Insects have good vision and can see clearly in the UV region of the e.m spectrum
34
Which part of a plant is where pollen is produced?
The anther
35
What do pollen grains contain?
The male gametes
36
Where are pollen grains formed?
Within the pollen sacs
37
Describe the pollen sacs in an anther
Their ranged in two parts, side by side
38
Where specifically in an aether are pollen grains produced?
In the pollen sacs
39
Describe the development of pollen in the anther
Pollen mother cell (diploid, 2n)
Undergoes mitosis to produce many of them
1st and 2nd meiotic division occur to form a tetrad of 4 haploid (n) pollen grains
Mitosis of these nuclei occur and they mature - DNA is replicated and separated into 2 haploid nuclei in each pollen grain
This forms 4 mature pollen grains
40
Features of a mature pollen grain
Tube nucleus (n)
Generative nucleus (n)
Thick sculptured wall - intine and exine
41
What does the cell wall of a pollen grain prevent from happening?
Prevents desiccation (drying out)
42
Why does the cell wall of a pollen grain prevent dessiction?
It’s waterproof and can survive in a dry environment
43
What is the cell wall of a pollen grain an adaptation to?
A terrestrial environment
44
What have pollen grains adapted to which animals haven’t? Explain
A terrestrial environment
Sperm cells have to stay in a fluid environment
45
Generative nucleus
Will fertilise the female gamete to form the zygote
During pollination, will divide by mitosis to form 2 male nuclei
46
Which nucleus in a pollen grain will fertilise the female gamete to form the zygote?
The generative nucleus
47
What will the tube nucleus do in a pollen grain?
Will form the pollen tube, which is part of fertilisation
48
Explain the purpose of the tube nucleus of a pollen grain and how it works
When the pollen grain lands on the stigma, the gamete has to be transported from the pollen grain to the female gamete
Therefore, the tube grows towards the ovary in the ovule to transfer the male gamete to the female gamete
This is why, in the pollen grain, there is a nucleus to start the growth of the pollen tube towards the female gamete
49
Explain dehiscence
When the pollen grains are mature and ready to be released, the outer layers of the anther dry out.
This causes tension on the stromium and the walls of the anther pull apart, releasing the pollen
This is known s dehiscence
50
What is it called when the outer layers of the anther dry out, causing tension on the stromium and the walls of the anther pulling apart, releasing the pollen?
Dehiscence
51
Tapetum
Tissue around the pollen sac involved in providing nourishment and nutrients for the developing grains
52
What have plants evolved to do over time?
Live on dry land
53
How have plants evolved to live on dry land?
- water proof cell wall
-seeds
54
Where exactly does the female gamete develop in flowering plants?
In the ovule in the ovary in the carpel
55
In which part of the ovule do female gametes develop in flowering plants?
In the embryo sack
56
What is the embryo sack of the ovule surrounded by?
The nucellus
57
Nucellus
A mass of cells that gives nutrients to the cells in the embryo sack
58
What surrounds the nucellus in the ovule?
Two protective integuments
59
Via what does the pollen go into the ovule when fertilisation occurs?
Via the micropyle
60
What is the whole ovule attached to the plant to and carried on?
A short stalk called the funiculus
61
What does the funiculus do?
Carried nutrients when developing from the plant to the ovule
62
What does one cell in the nucellus of the ovule develop into?
The megaspore mother cell (2n)
63
Explain the stages of the development of the embryo sac
1. Start with the megaspore mother cell (diploid)
2. This undergoes meiosis to form 4 haploid cells. 3 of the 4 cells degenerate. Only 1 forms the embryo sac
3. The inner cell grows to form the megaspore or embryo sac (haploid)
4. When grown, the cell undergoes 3 mitotic divisions. The DNA has been replicated and it’s the megaspore nucleus that undergoes the divisions in order to form 8 haploid (n) nuclei.
5. 2 nuclei move to the centre of the embryo sac to form polar nuclei (n). The remaining nuclei develop cytoplasm around them and become separated by cell walls.
64
Things to label on an embryo sac
Antipodal cells
Polar nuclei
Egg cell (ovum)
Synergies
Micropylar end
65
Things to label on an ovule
Chalaza
Nucellus
Funiculus
Embryo sac
Integuments
Micropyle
66
Which cells in the embryo sac play no further role after development and have no part in fertilisation?
The thee antipodal cells
67
Which cell in the embryo sac develops into the female gamete?
One cell nearest micropyle (the centre cell)
68
What do the other two cells nearest the micropylar end in an embryo sac form?
Synergids that degenerate after fertilisation
69
When do the synergids in an embryo sac degenerate?
After fertilisation
70
Pollination
The transfer of pollen from the anther to the stigma
71
Self pollination
The transfer of pollen from the anther to the stigma of the same flower
72
Cross pollination
Transfer of pollen from the anther of one flower to the stigma of a different flower
73
Stamen
Pollen producing part of a flower
74
How is an anther different to a stamen?
The anther is the specific part of the stamen where pollen is produced
75
Pistil
Contains several carpels
76
Explain briefly how cross pollination can occur
1.) pollen from stamens stick to a bee as it visits a flower to collect food
2. The bee travels to another plant of the same type
3. Pollen on the bee sticks to a pistil of a flower on the other plant
77
What type of pollination is the most advantageous in terms of genetic diversity?
Cross pollination
78
What is cross pollination the most advantageous in terms of?
Genetic diversity
79
What have plants done due to cross pollination being the most advantageous method of pollination in terms of genetic diversity?
Have evolved methods to make it more likely to cross pollinate than to self pollinate
80
Why are the things we can mention when comparing self-pollination and cross-pollination?
Transfer of pollen
Fertilisation
Genetic variation
Harmful alleles
Genome preservation
81
Compare self-pollination and cross-pollination in terms of transfer of pollen
Transfer of pollen from the anther of a flower to the mature stigma of the same flower, or another flower on the same plant of the same species (it’s the same plant so it’s self-pollination)
Vs
Transfer of Poland, from the answer of a flower to the mature, stigma of another flower on another plant of the same species
82
Compare self-pollination and cross-pollination in terms of fertilisation and what they lead to
Self-pollination leads to self-fertilisation which leads to inbreeding
Cross-pollination leads to cross-fertilisation which leads to outbreeding
83
Compare self-pollination and cross-pollination in terms of genetic variation
Both:
Genetic variation dependent on
-crossing over during prophase I or meiosis
-independent assortment during metaphase I of meiosis
-mutation
Cross-pollination also has the additional:
-combining genotypes of gametes from two different individuals
84
Compare self-pollination and cross-pollination in terms of genetic variation
Less, more
85
Compare self-pollination and cross-pollination in terms of the risk of harmful combinations of alleles
Self-pollination: greater chance of two potentially harmful recessive alleles combining
Cross-pollination: reduced chance of producing harmful combinations of alleles
86
Compare self-pollination and cross-pollination in terms of genome preservation
Successful genomes are preserved, which is an advantage in a stable environment but a disadvantage if the environment changes suddenly
Advantageous in terms of evolution because if the environment changes suddenly, it is likely that there are individuals within the population with a combination of alleles that will allow the species to survive
87
What do gardeners often do in order to preserve characteristics?
Self-pollinate
88
List the adaptations of flowers to promote cross-pollination
1. Chemical self-incompatibility
2. Irregular flower structure
3. Dichogamy
4. Monoecious plants
5. Dioecious plants
89
Chemical self-incompatibility
Gametes from the same parent plant are unable to fuse and form a zygote or, if the zygote forms, then it fails to develop = prevents self-fertilisation
90
Dichogamy
Anthers and stigmas mature at different times on the same plant so self-pollination can’t occur
91
Example of flowers with irregular flower structures
Primroses
92
Monoecious plants
Have separate female and male flowers on the same plant
93
Example of a monoecious plant
Hazel
94
Dioecious plants
Have separate male and female plants
95
Example of a dioecious plant
Willow
96
Where are primroses found?
Found in hedgerows and sides of paths
97
Why are there 2 versions of primroses?
An adaptation to ensure that cross-pollination occurs
98
2 varieties of primroses
Pin eyed primula
Thrum eyed primula
99
What’s the difference between the pin eyed and thrum eyed primulas?
The length of the stigma and anther are different in both
100
Length of style and anthers in pin eyed primula
Long style, short anthers
101
Length of style and anthers in thrum eyed primula
Long anthers, short styles
102
Where are the anthers in thrum-eyed primulas?
Close to the opening as they’re long
103
What is the difference between style and stigma?
Stigma is the end bit of the style
104
What variety of primroses will pollen grains not fall into and why?
Pin-eyed since the stigma is above the anthers
105
At what level do insects tend to pollinate a sigma?
On the same level as anthers that they collected the pollen from
106
Where do pollen grains tend to be transferred in primroses?
From pin eyed to thrum eyed and vice versa
107
Explain how pollen would be transferred to thrum eyed primroses
Bees tongue extends to the base to obtain nectar
Brushed against the anther, picking up pollen
The bee flies to the next flower, a pin-eyed one and sticks its head in
Pollen grains rub off onto the stigma and start fertilisation
108
What would happen if pollination was attempted to occur between 2 pin-eyed flowers?
Pollen grains won’t fall onto it so self-pollination is less likely
109
Explain the mutual relationship between Darwin’s Hawk mother and an orchid
The orchid has a long tube protruding from it which has the nectary at the very bottom
Darwin predicted that there must be an insect with a tongue long enough to be able to reach this, which there was
His prediction was correct. He knew that the plant wouldn’t exist following evolution if an insect hadn’t developed to get its pollen and pollinate it
110
What is fertilisation?
The process in which a male gamete fuses with a female gamete to form a zygote
111
Where is the female game in flowering plants?
In the ovule, protected within the ovary
112
What undergoes mitosis during double fertilisation and what does this form?
The generative nucleus
Produced two haploid male gametes in the pollen grain
113
How are the two haploid male gametes formed by the mitosis of the generative nucleus during double fertilisation delivered?
By the pollen tube
114
How many cells does the pollen tube initially contain?
Two haploid cells - the generative cell and the tube cell
115
What is the location of double fertilisation?
The embryo sac
116
What is within the embryo sac for double fertilisation?
2 haploid polar nuclei
Also the haploid female gamete
117
What will the 2 male nuclei fuse with during double fertilisation?
The haploid polar nulei
The haploid female gamete
118
Explain double fertilisation
1. When a compatible pollen grain lands on the stigma, it germinates in the sucrose solution secreted by the stigma and produces a pollen tube
2. The pollen tube nucleus is at the tip of the tube, with the two male nuclei behind
3. The pollen tube grows out of the pollen grain through a gap in the cell wall, called a pit, and down the style up a gradient of chemoattractants e.g - GABA from the ovule.
The pollen tube nucleus codes for the production of hydrolyses including cellulases and proteases, and it digests its way through the tissues of the style. The products of digestion are used by the growing pollen tube.
4. The pollen tube grows through the gap in the integuments, the micropyle, and passes into the embryo sac
5. The pollen tube nucleus disintegrates, presumably having completed its function of controlling the growth of the pollen tube
6. The tip of the pollen tube opens, releasing the 2 male gametes into the embryo sac
7. The male gametes enter the cytoplasm of the synergid
8. The synergid breaks down
9. The male and female gametes are haploid. One of the male gametes fuses with the female gamete, the oosphere, to form a zygote which is diploid
10. The other male gamete fuses with the diploid polar nucleus to form a triploid nucleus. This triploid nucleus is the endosperm nucleus. When is subsequently divides repeatedly by mitosis, it generated the endosperm tissue, which takes over from the nucellus in providing nutrition for the developing embryo
119
Triploid nucleus formed during double fertilisation
Endosperm nucleus
120
When does the pollen tube nucleus disintegrate during double fertilisation?
Presumably having completed its function of controlling the growth of the pollen tube
121
Name for the female gamete involved in double fertilisation
Oosphere
122
What does the ovule do at the end of double fertilisation?
Develops into a seed
123
Why is double fertilisation called this?
Two fusions have occurred - one to form the zygote and one to form the endosperm.
124
What is double fertilisation unique to?
Seed plants
125
How many pollen grains germinate successfully during double fertilisation and what happens to the others?
Only one, the others disintegrate
126
Roles of the tube nucleus in double fertilisation
Controls and directs the growth of the tube nucleus
DNA codes for enzymes that digest their way through the tissues of the style. This creates a path for the growing pollen tube and the products of digestion are used by the growing pollen tube.
127
What happens to the diploid zygote following double fertilisation?
Develops into the embryo plant
128
What happens to the triploid endosperm cell following double fertilisation?
Develops into the food reserve in the seed
129
How does the triploid endosperm cell develop into the food reserve in the seed following double fertilisation?
When the seed generate, the embryo can absorb the food and grow
130
What happens to the integuments following double fertilisation?
Develop into the seed-coat (testa) - outer layer of seed
131
Name for the seed-coat formed by integuments after double fertilisation
Testa
132
What happens to the ovary wall following double fertilisation?
Can grow and sweet in order to develop into a fruit
133
Where is the ovary wall?
Outside the ovules
134
Testa
Seed-coat that forms from the integuments following double fertilisation
135
Why is fertilisation in plants referred to as double fertilisation?
1 male nucleus fuses with the female gamete to form a diploid zygote
1 male nucleus joins with the 2 polar nuclei to form the triploid endosperm nucleus
136
What do we need to remember to always refer to when describing stages of fertilisation?
Refer to the number of sets of chromosomes
137
Stigma
The receptive surface for pollen
138
Things to label on an ovary
Epidermis
Ovary wall
Ovule
Funicle
Nucellus
Embryo sac
139
What forms in plants after fertilisation?
Seeds
140
What are seeds unique to?
Plants
141
What are the 2 purposes of seeds?
They’re part of the plat’s reproductive system but also act as a survival capsule of the plant
142
Why are seeds described as “survival capsules” for plants?
There aren’t always favourable conditions for the growth of plants, for example during long, dry seasons in some countries that involve very little rain, leaving not much water in the soil. Also during the winter in temperate countries
143
When are seeds the most useful as survival capsules?
During long, dry seasons in some countries that involve very little rain
During the winter in temperate countries
144
Dormant seeds
Alive but not growing
145
Describe seeds when they are dormant
Remain lime this in the soil for long periods of time where their metabolism is almost at zero
146
“Long periods of time” that seeds can remain dormant for
Years in some cases
147
When will dormant seeds germinate and grow?
When the conditions are right
148
2 main types of seeds
Dicotyledon seeds
Monocotyledon seeds
149
Name for dicotyledon seeds
Vicia faba
150
Monocoyledon seeds name
Zea mays
151
Example of a dicotyledon seed
Broad beans
152
Example of a monocotyledon seed
Maize
153
What are the things we label on seeds (dicotyledon and monocotyledon)?
Testa
Hypocotyl
Plumule
Hilum (scar of the funicle) (dicotyledon only)
Micropyle
Radicle
Cotyledon
Funicle (monocotyledon only)
Endosperm (monocotyledon only)
Testa and pericarp fused (monocotyledon only)
154
How come the micropyle is still in the seed and where?
The pollen tube grew into the ovule through the micropyle and it’s still in the testa
155
Micropyle function in seeds
Allows the seed to draw in water during germination
156
Plumule in seeds function
When the seed germinates, it develops into the stem and leaves of the plant - embryonic shoot with first leaves
157
Radicle of seeds function
When the seed germinates, it develops into the roots - embryonic root
158
What takes up most of the inside of a monocotyledon seed?
The endosperm
159
What does the endosperm in a seed do?
It stores starch which provides a food source for the growing embryo
160
When was the endosperm of a seed generated?
During double fertilisation
161
Difference between the cotyledon in a dicotyledon and a monocotyledon seed
Monocotyledon —> only 1 and is smaller
162
Cotyledon in a seed function
The seed food reserve. When the embryo plant generates, it draws its nutrients from the cotyledon.
163
What is the testa in a seed?
The seed coat
164
Testa in seeds description
The seed coat. Developed from the integuments that were around the ovule.
165
What did the testa of seeds develop from?
The integuments that were round the ovule
166
What are the 2 halves of a peanut seed?
The cotyledons
167
What are peanuts in reality and why?
Beans,not nuts
They’re related to the same family as legumes (have root nodules etc.)
168
Which part is the fruit when bean seeds grow in a pod and why?
The pod since it formed from the ovary wall
169
Which part are the seeds when beans grow in a pod?
The beans
170
What makes something a fruit?
Formed from the ovary wall
171
Why would bean seeds turn black and under which conditions would this be?
If we were to open a bean seed, remove their testa and separate the cotyledon before putting iodine on them, they would turn black since they’re full of starch
172
Why do dicotyledon seeds not have an endosperm?
The cotyledons are small to begin with but then absorb the nutrients form the endosperm as they develop before taking over and filling the whole seed
173
How do cotyledons end up taking over the whole of dicotyledon seeds?
They’re small to begin with but then absorb the nutrients from the endosperm as they develop before taking over and filling the whole seed
174
What form the embryo in monocotyledon seeds?
The plumule and the radicle
175
Pericarp of a monocotyledon seed description
Forms the outer coat of the monocotyledon. It is the fruit of the plant.
176
Fruit of the monocotyledan
Pericarp
177
Why is the pericarp the fruit of monocotyledon seeds?
It’s formed from the ovary wall
178
What colour is the endosperm of monocotyledon seeds and what is the significance of this?
White
Is used to form cornflour and is nutritious
179
What are the inner parts of monocotyledon seeds formed from?
The ovule
180
What is the name of the layer that’s only in monocotyledon seeds?
Aleurone layer
181
What does the aleurone layer contain?
Proteins and enzymes
182
Describe the enzymes of the aleurone layer when a seed is dormant
Inactive
183
When are the enzymes of the aleurone layer in monocotyledon seeds active and what does this lead to?
As soon as germination starts
They break down the food reserve (starch in the endosperm). This allows the embryo of the plant to absorb the nutrients and grow.
184
Purpose of the active enzymes of the aleurone layer during germination of a monocotyledon seed
They break down the food reserve (starch in the endosperm) and this allows the embryo of the plant to absorb the nutrients and grow
185
Food reserve in a monocotyledon seed
Starch in the endosperm
186
How does the embryo of a monocotyledon seed start absorbing nutrients and grow?
When the enzymes in the aleurone layer activate during germination and break down the food reserve (starch in the endosperm)
187
Why is seed dispersal important?
Since seeds are part of a plants reproductive cycle
188
What needs to happen for seeds to play a part in a plants reproductive cycle?
They need to be dispersed
189
Why is it important that seeds disperse?
The seeds need to move away from the parent plant so that you don’t get lots of seeds in the same area competing against each other
190
How do seeds ensure that you don’t get lots of seeds in the same area competing against each other?
Have evolved strategies to disperse
191
What are the different ways in which plants disperse seeds?
Wind
Animals
Water
Explosion
192
Two examples of seeds that are dispersed by wind
Dandelion seeds
Sycamore seeds
193
How are dandelion seeds dispersed by the wind?
Have a feathery stalk
194
How have sycamore seeds adapted to be better dispersed?
They spin as they fall as they have veins that rotate them when they catch the air. This slows down the rate of fall so that they can be carried further by the wind.
195
Main way seeds are dispersed using animals
Have spoken structures so that they can latch onto animal fur
196
Explain why some seeds are colourful in terms of dispersal
Attract animals to eat them. These will have a tough outer coat so as to survive the animals digestive system. They will then be excreted in the faeces and the seeds will be distributed from the parent plant (assuming that the bird has flown away)
197
Explain the relationship between jays and oak trees
Jays cause seed dispersal
They like acorns however all of the acorns become available at the same time of year (October). Therefore, the birds stored acorns for feeding all over the winter. They do this by burying them so that squirrels etc don’t eat them. The jays find approximately 60% of these buried acorns so the other 40% of them stay in the soil and grow into new oak trees in the spring
198
Explain how coconut seeds are dispersed by water
Have a buoyant husk on the outside (fibres which catch air). We usually see coconuts growing on beaches since when the coconut falls, it rolls into the sea and is carried by the tides to grow somewhere else
199
Give an example and explain a plant that disperses its seeds via explosion
Himalayan Balsam
When touched, the seeds explode open. These plants are often found by rivers therefore the seeds are then transported into the river and are carried away by the water.
200
Compare the roots of the plant of a monocotyledon and a dicotyledon
Fibrous, tap root
201
Compare the veins of the plants of monocotyledon and dicotyledon
Parallel, netlike
202
Extra things to label on a fully grown monocotyledon plant
Leaf sheath
203
Extra things to label on a fully grown dicotyledon plant
Withering cotyledons
204
What is the major factor that prevents germination?
The water content of seeds being very low
205
What does the water content of seeds being very low prevent?
Germination
206
Describe the soil during dry seasons and what this prevents
Very dry, prevents germination
207
How will seeds remain until suitable conditions are present?
Dormant
208
All of the conditions required for seeds to no longer remain dormant and for germination to occur
Water to mobilise enzymes, for transport of dissolved substances, and to vacuolate cells to make them turgid and swell cotyledons
Oxygen for aerobic respiration and ATP for metabolism
Suitable temperature for enzymes to operate + speeds up rate of diffusion
209
Explain what germination involves
The rapid onset of biochemical activity and growth of a seedling until the plant can carry out photosynthesis and become independent of the food stores contained in the cotyledons or endosperm
210
What can’t a seed do when it’s first germinated and what must it do instead?
Can’t photosynthesise until it’s grown leaves so it’s dependent on the cotyledons
211
Explain germination in a non-endospermic seed (dicotyledon seed)
When there’s enough water and the temperature is right, the seed starts to germinate…
1. Water is imbibed (taken in) through the micropyle (a hole in the testa)
2. The cotyledons swell and the testa splits, allowing entry of more water and oxygen for aerobic respiration
3. Starch and protein reserves in the cotyledons are hydrolysed
4. Products of hydrolysis are used as:
- a source of energy for respiration - glucose
- growth of the plumule and radicle - amino acids
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What does the plumule of a plant develop into?
Shoots
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What does the radicle of a plant develop into?
Roots
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Example of a non- endospermic seed
Viscia faba
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Explain the germination of a monocotyledon seed
1. Following the imbibing of water gibberellin (gibberellic acid) - a type of hormone - is released by the embryo
2. The gibberellin diffuses to the aleurone layer (the outer layer of the endosperm) which contains protein. Gibberellin induces the production of hydrolytic enzymes e.g amylase
3. The hydrolytic enzymes diffuse into the inner layer if the endosperm and catalyse the breakdown/hydrolysis of stored nutrients here (e.g - starch)
4. Glucose and other breakdown products of the stored nutrients diffuse into the embryo
5. They are used for aerobic respiration and growth of the radicle and plumule
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Method for the experiment involving germinating seeds in starch agar
1. Germinating seeds cut in half (use boiled seeds)
2. As the seeds germinate, they produce amylase that digests the starch agar
3. By flooding the plate with iodine, we will see clear zones where the enzymes have digested the starch/starch has been hydrolysed
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What are the clear zones in the germinating seeds on starch agar experiment?
This is where the enzymes (amylase produced when germinating) have digested the starch and the starch has been hydrolysed
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What can we see in the areas where the enzymes have digested the starch with germinating seeds on starch agar?
Clear zones
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How can we measure how different factors affect the germination of plants using the germinating seeds in starch agar experiment?
By measuring the diameter of the clear zones around the germinating seeds
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Which factors can we compare to see their effects on germination in plants using the germinating seeds on starch agar experiment?
Use different varieties of seed (keep other variables the same)
Use different temperatures
Use different oxygen partial pressures
Initially soak the seeds for different times
Use different light intensities (some seeds need light to germinate)
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Why do only fertilised ovules develop into fruit?
No zygote/no fertilisation of the egg cell means no stored food. This saves the plant resources and energy for other processes.
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Will flowers on the same plant be genetically identical? Explain
Yes since they’re produced by mitosis and are clones
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What do we need to ensure that we do when comparing different varieties of seed in the germination of seeds on starch agar practical?
Keep other variables the same
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Why could we use different light intensities as a factor to compare the germination of plants in the germinating seeds on starch agar practical?
Some seeds need light to germinate
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What does amylase digest starch in cotyledons into (dicotyledon seeds)?
Amylase digest starch in cotyledons to maltose
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What are proteins/fats in dicotyledon seeds broken down into?
Amino acids
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What does Gibberellic acid to do to protein?
Break down into amino acids
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What are amino acids used for (when broken down by Gibberellic acid in monocotyledon seeds)?
To synthesise enzymes such as amylase
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What does amylase do to starch in the endosperm of monocotyledon seeds?
Breaks it down into maltose
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Which enzyme digests starch?
Amylase
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What is starch digested into by amylase?
Maltose
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What are amylase enzymes synthesised from?
Amino acids
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What breaks down starch in the endosperm of monocotyledon seeds into maltose?
Amylase
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What is one of the remaining nuclei formed from the 3 mitotic divisions of the one cell from the meiosis of the megaspore mother cell?
The egg cell
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Why can seeds still germinate?
Because of food stores
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Difference between fruit and seed
Fruit = ovary wall and testa fuses
Seed = only testa
