Lecture 3 - DA

Question 1

What are 8 factors affecting community structure?

Answer 1

Light
Temperature
Water
Wind
Nutrients
Slope/aspect
Biotic
Fire

Question 2

What is a community structure determined by?

Answer 2

The environment and species interactions.

Question 3

What always happens to growth rates? Name 3 reasons as to why this may be.

Answer 3

They always plateau.

May be due to exhausted nutrients, the population reaching a certain level, or lack of space.

Question 4

What does light primarily affect, and how?

Answer 4

Affects primary producers, by affecting photosynthesis.

Question 5

What is the difference between gross level and net photosynthesis? What happens if there is no net photosynthesis?

Answer 5

Gross level - max capacity of photosynthesis for a given species.
Net - net sugar gained per day from photosynthesis after expenditure on cellular respiration.
No net gain means no growth.

Question 6

What is the light compensation point, and what value does the net gain have?

Answer 6

Point at which the plant breaks even on sugar production to meet cellular respiration requirements with photosynthesis.
Net gain is 0 at this point.

Question 7

Do all plants have the same light compensation point?

Answer 7

No, it differs among species.

Question 8

Describe the two types of plants in the context of sunlight.

Answer 8

Sun plants - grows well in full sunlight

Shade plants - work with very little light

Question 9

Where are shade plants often found?

Answer 9

Understory.

Question 10

What happens to the net photosynthesis of shade plants? Why is this so?

Answer 10

It will eventually plateau. Does so due to negative feedback, where more sugar is made than can be transported back, essentially stalling.

Question 11

What is the net photosynthesis like in sun plants? Do they require more or less light to achieve the light compensation point compared to shade plants? Explain why.

Answer 11

Net photosynthesis increases almost linearly.
They need more light than shade plants to reach the light compensation point. This is because they need energy to uptake nutrients through their roots, as well as reflecting light.

Question 12

What conditions are sun plants adapted to live in? Why do they not survive in low light conditions? What will happen if you put a shade plant into a high light intensity condition (ie a desert)?

Answer 12

Sun plants are adapted to live in desert-like conditions with high light intensity.
When put into low light, too much light is reflected due to their adaptations, and will die.
Shade plants cannot reflect enough light, and will die under high light intensity.

Question 13

What are the leaves like for shade plants vs a sun plant?

Answer 13

Shade plants - often thin, soft leaves

Sun plants - often thick, hard leaves

Question 14

How can the leaf hardness of sun plants explain their high light requirement?

Answer 14

Their leaves are hard due to the sclerenchyma cells, which are dead.
As they are dead, no photosynthesis occurs, requiring them to be exposed to more sunlight.

Question 15

How can temperature affect an organism’s lifecycle?

Answer 15

Some species require certain temperatures to complete a lifecycle.

Question 16

Is the optimum temperature of a species a good guide to its tolerance? Give an example.

Answer 16

No. Thermophilic fungi exist in Antarctica, that grow well at 45*C.

Question 17

Does the region where an organism live act as a good guide to its optimum requirements (on ie temperature)?

Answer 17

No. Thermophilic fungi exist in Antarctica, that grow better at 45*C.

Question 18

Where do C4 plants usually live, and how are the different to C3 plants?

Answer 18

Hotter conditions. Are able to store carbon in an intermediate step, and use later on if the temperature is too hot.
C3 cannot do this in hot conditions, and will lose too much water trying to get CO2.

Question 19

What affects water availability?

Answer 19

Salinity.

Question 20

Name 3 ways a plant can minimise water output/loss.

Answer 20

Waxy cuticle
Hairy surfaces
Sunken stomata

Question 21

What are 2 ways some can species fight for water?

Answer 21

Underground through their roots, may produce toxic substances.
Plants may outgrow others, by pushing them to understory, and more photosynthesis through higher canopy cover, allowing deeper roots

Question 22

Order the following from most water, to least:
Open forest
Mallee
Desert
Grasslands
Shrublands (low and tall)
Rainforest
Closed forest

Answer 22

Rainforest
Closed forest
Open forest
Mallee
Shrublands (tall, then low)
Grasslands
Desert

Question 23

Are high wet conditions always favourable?

Answer 23

No, some species are susceptible to diseases like fungi/bacteria.

Question 24

What are some adaptations that plants and animals can have to high salinity conditions?

Answer 24

Plants - salt glands on their surface to excrete the salt they uptake.
Some animals have salt glands on their beaks that concentrate and excrete salt.

Question 25

What do species that grew close to salty coasts have in common, and why?

Answer 25

They are similar worldwide as their seeds are carried by ocean currents, deposited onto other continents.

Question 26

What strong effect does wind have, and why?

Answer 26

Interacts with water, has a strong drying effect due to greater transpiration.

Question 27

Aside from drying, how else can wind negatively affect plants?

Answer 27

Causes sandblasting, which will remove the waxy coating, making them more susceptible to disease.

Question 28

Is wind ever a good factor? Are plants often adapted to high wind conditions?

Answer 28

No, like salt, it is rarely good. Plants rarely adapt.

Question 29

Where are nutrients primarily found?

What are 5 factors affecting this?

Answer 29

In the soil.
Affected by the minerals and hardness of the soil, as well as weathering factors such as water and wind.
pH also affects the solubility of ions.

Question 30

What is the ability to store nutrients measured by?

Answer 30

Cation exchange capacity - CEC.

Question 31

What is organic matter typically made of in soil, what charge does it have, and how does high clay content affect cations?

Answer 31

Organic matter is made of lignin, with a net negative charge, binding cations.
High clay content has more sites to bind cations as well.

Question 32

What is a mesophytic habitat?

Answer 32

Habitat with best conditions, ie water, nutrients, soil type etc.

Question 33

Which will have higher diversity - habitat with ideal conditions, or habitats with nutrient-poor conditions? Why is this so?

Answer 33

Mostly in nutrient-poor habitats, because no single species dominates, an even playing field favours diversity.

Question 34

Do rainforests have nutrient rich or poor soils?

Answer 34

Poor.

Question 35

How does slope/aspect interact with water?

Answer 35

Allows/inhibits drainage.

Question 36

How does slope/aspect interact with temperature?

Answer 36

Plants covering other plants due to slope by hanging over them will lower temperatures.

Question 37

Slopes facing which two directions will have less cover? Which two have more?

Answer 37

Less cover
North, West
More cover
South, East

Question 38

What are some biotic factors affecting community structure?

Answer 38

competition between species, certain habitats are dominated by one species.

Question 39

Describe the predator-prey relationship (5).

Answer 39

• Prey population increases
• Predator population increases
• Too much predation occurs
• Prey population collapses
• Predator population collapses
• A cycle