Unit 4 - Biology: Plants, hormones and reproduction

Question 1

State the functions of xylem and phloem

Answer 1

Xylem: water and soluble salts transport. Water moves the soil to the xylem in the root down a concentration gradient. Water moves up the xylem by CAPILLARY ACTION. One-way flow. Cells dead.

Phloem: organic materials transport from the leaves to all other parts of the plant (eg leave to roots, leaves to developing fruit). Two-way flow. Cells are alive.

Question 2

Identify the positions of xylem tissues as seen in transverse sections of unthickened, herbaceous, dicotyledonous roots, stems and leaves.

Answer 2

Draw the diagrams

Question 3

Identify root hair cells, as seen under the light microscope, and describe their functions; relate their structure & function to their surface area and to water and ion uptake.

Answer 3

Draw root hair diagram

Function: absorbs water and mineral ions from the soil.

Large surface area - more area for osmosis
- more water and ions absorbed
- more friction: - stays in ground
- stable
-provides stability
No chloroplasts - no sunlight = no need for chloroplasts because it cannot photosynthesise.

Question 4

Investigate, using a suitable stain, the pathway of water through the above-ground parts of a plant.

Answer 4

Food dye.

Question 5

Define transpiration

Answer 5

Evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, through the stomata.

The movement of water molecules through the plant. Up from the roots, through the xylem vessels and evaporating out through the stomata in the leaves.

Question 6

Describe the effects of variation of temperature, humidity and light intensity on transpiration rate.

Answer 6

Light intensity
Light intensity up = transpiration up
More light = more photosynthesis therefore more water used.
The stomata open wider to allow more CO2 into the leaf for photosynthesis.

Temperature
Temperature up = transpiration up
Higher temperature = more evaporation therefore more transpiration.
Evaporation and diffusion are faster at higher temperature.

Wind
Wind up = Transpiration up
More diffusion therefore more transpiration. Water vapour removed quickly by air movement, speeding up the diffusion of more vapour out of the leaf.

Humidity
Humidity up = transpiration down.
Less diffusion therefore less transpiration. Concentration gradient is smaller. Leaf is already surrounded by moist air.

The rate of transpiration is determined by the limiting factor. This is the component of transpiration which is the “least”. If this limiting factor is increased then the rate of photosynthesis will increase until another factor limits the rate.

Question 7

Define hormone

Answer 7

A chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver.

Question 8

State the role of the hormone adrenaline in chemical control of metabolic activity

Answer 8

• increasing blood glucose concentration and pulse rate
• produced in the adrenal gland
• decreases reaction times
• increases breathing rate
• diverts blood to muscles (away from eg digestive system)
• hairs stand up
• generated in nervous or frightening situations.

Question 9

Give examples of situations in which adrenaline secretion increases

Answer 9

Fight or flight situations, stage fright.

Question 10

Define and investigate GEOTROPISM and PHOTOTROPISM

Answer 10

Geotropism - growth in response to the direction of GRAVITY.
Positive geotropism at root tip - grows towards gravity - more chance of finding moisture.
Negative geotropism at stem tip - grows away from gravity - more chance of finding light.

Phototropism - growth in response to the direction of LIGHT
Positive phototropism at stem tip - growth towards light to get maximum light for photosynthesis.
Negative phototropism at root tip - growth away from light - less chance of drying out.

Question 11

Explain the chemical control of plant growth by auxins including geotropism and phototropism in terms of auxins regulating differential growth.

Answer 11

Auxin: a plant hormone responsible for controlling the direction of growth of root tips and stem tips in response to different stimuli including light and gravity.

It is made the the tips of stems and roots. It controls the rate of plant growth.

Phototropism - auxin production on the side opposite to light to make that side grow faster to face the sun.
In a shoot, the side containing auxin grows faster, however in the roots, the shaded side contains more auxins, but this side grows slower, bending the root away from light.

Geotropism - auxins production on the bottom side, this causes the root grow less on the bottom side, bending in the direction of the force of gravity.
In a horizontal shoot, the bottom side contains more auxins than the top, This makes the bottom side grow more than the top side, causing the shoot to bend against the direction of gravity.

Auxins are always placed in the shadiest side, this is because the side with the sun destroys the auxin in that side of the plant.

Question 12

Define asexual reproduction

Answer 12

The process resulting in the production of genetically identical offspring from one parent.

• fertilisation not involved.
• no male/female
• splitting of a cell
• gametes not involved
• used by plants

Question 13

Define sexual reproduction

Answer 13

The process involving the fusion of haploid nuclei to form a diploid zygote and the production of genetically dissimilar offspring.

• gametes involved
• used by mammals
• often two parents, sometimes only one
• fertilisation involved
• young genetically different from each other, and from parent or parents.

Haploid = 23 chromosomes 
Diploid = 23 PAIRS after fertilisation
Zygote = fertilised cell

Each diploid cell contains 2 copies of each chromosomes - one from the mother, one from the father.

Question 14

Identify and draw the sepals, petals, stamens, anthers, carpels, ovaries and stigmas of a insect pollinated flower.

Answer 14

Draw and label.

Question 15

State the functions of the sepals, petals, anthers, stigmas and ovaries.

Answer 15

Sepal: Leaf-like structure at flower base, protects young flower bud

Petals: Located in and above the sepals, often large and colourful, sometimes scented, sometimes producing nectar. Often serve to attract pollinators to the plant.

Anthers: Structure which produces pollen grains

Stigma: sticky top of carpel/style, serves as a receptive surface for pollen grains.

Ovaries: enlarged base of the carpel containing the ovule(s). The ovary matures to become a fruit.

Question 16

Define pollination

Answer 16

The transfer of pollen grains from the male part of the plant (anther of stamen) to the female part of the plant (stigma).

Question 17

Name the agents of pollination

Answer 17

Flying insects (bees) and wind

Question 18

Compare the different structural adaptations of insect-pollinated and wind-pollinated flowers.

Answer 18

Insect pollinated:

• large, colour pedals to attract insects
• sweetly scented - attract insects
• usually contain nectar - attract insects
• moderate quantity of pollen - less wastage than with wind pollination.
• pollen often sticky/spiky to stick to insects
• anthers firm and inside flower - to brush again insects
• stigma inside flower so insects brush against it
• stigma has sticky coating so pollen sticks

Wind pollinated:

• small petals, often dull/green/brown because there is no need to attract insects
• no scent - no need to attract insects
• no nectar - no need to attract insects
• pollen produced in great quantities because most does not reach another flower.
• pollen light and smooth - so it can be blown in the wind and stops it clumping together
• anthers loosely attached and dangle out - to release pollen into the wind
• stigma hangs out - to catch the drifting pollen
• stigma feathery or net-like to catch drifting pollen.

Question 19

Investigate and state the environmental conditions that affect germination of seed

Answer 19

Water - allows the seed to swell up and the embryo start growing

Oxygen - so that energy can be released for germination

Suitable temperature - germination improves as temperature rises (up to a maximum)

Question 20

Identify on diagrams of the male reproductive system, the testes, scrotum, sperm ducts, prostate gland, urethra and penis, and state the functions of these parts

Answer 20

Testis - sperm are made here. Inside the scrotum
Scrotum - contains testes
Sperm duct - carries sperm from the testicle to the outside.
Prostate gland - makes a fluid containing citric acid, which the sperms also use as an energy source, as well as fructose.
Urethra - links kidneys to bladder - carries urine
Penis - male external genitalia

Question 21

Compare male and female gametes in terms of size, numbers and mobility.

Answer 21

Sperm: millions, small, very fast - motile (capable of movement)
Egg: usually 1, very big, stationery (moved by cilia in fallopian tubes.

Question 22

Identify on diagrams of the female reproductive system, the ovaries, oviducts, uterus, cervix and vagina, and state the functions of these parts.

Answer 22

Ovaries - eggs are made and stored and released
Oviducts - or fallopian tube. Allow egg to travel to uterus by cilia-covered cells. Can contract rhythmically to produce rippling movements.
Uterus - where fertilised egg implants
Cervix - top of vagina, allow flow of menstrual blood from the uterus into the vagina, and direct the sperms into the uterus during intercourse.
Vagina - where sperm is deposited during intercourse.

Question 23

Describe the menstrual cycle in terms of changes in the uterus and ovaries

Answer 23

The menstrual cycle in women is a recurring process in which the lining of the uterus (womb), is prepared for pregnancy, and if pregnancy does not happen, the lining is shed at menstruation.

Several hormones control this cycle, which includes controlling the release of an egg each month from an ovary, and changing the thickness of the uterus lining. These hormones are secreted by the ovaries and pituitary gland.

Question 24

Describe fertilisation

Answer 24

The joining of the nuclei of male gamete (sperm) and the female gamete (egg).

Fertilisation happens when a male gamete penetrates the wall of the female gamete.

Question 25

Outline early development of the zygote

Answer 25

The formation of a ball of cells that becomes implanted in the wall of the uterus.

A single sperm cell penetrates the mother’s egg cell, and the resulting cell is commonly called a ZYGOTE. A zygote contains all the genetic information necessary for one to become a child. Half of the genetic info comes from the egg, other half from the father’s sperm.

The zygote continues to divide, creating an inner group of cells with an outer shell. This stage is called BLASTOCYTE. The inner group of cells will form to become an embryo, while outer cells will become the membrane which will protect the embryo.

The blastocyte arrives at the womb (uterus) around day 5 and implants into the uterine wall on about day 6.

Question 26

Indicate the functions of the amniotic sac and amniotic fluid

Answer 26

The amniotic sac and amniotic fluid protect the embryo inside the womb from shocks of movement. It also protects the embryo from temperature changes of the mother. The fluid allows the baby to move freely. It allows for lung development as the baby begins to breathe amniotic fluid to strengthen his lungs and swallow fluid to develop the gastrointestinal tract.

Question 27

Describe the function of the placenta and umbilical cord in relation to exchange of dissolved nutrients, gases and excretory products.

Answer 27

Umbilical cord would carry dissolved food and oxygen to the baby as well as carry urea and CO2 away from the fetus.

The placenta ensures exchange between CO2 and oxygen in the baby’s bloodstream. This ensures that oxygen can be moved into the bloodstream and CO2 can be taken away. However, the placenta also ensures that other nutrients are allowed to pass to the baby and other wastes are removed.

Question 28

Describe the advantages and disadvantages of breast-feeding compared with bottle feeding using formula milk.

Answer 28

Breast feeding
ADVANTAGES
-Immunity/antibodies to baby
-Develops bond between mother and baby
-idea of composition matches baby's needs/easier to digest
-reduced risk of cancers
-cost

DISADVANTAGES

• problems producing enough milk
• cannot delegate to male partner
• drugs, nicotine/HIV may be transmitted
• inconvenience
• social issues

Bottle feeding
ADVANTAGES
-able to produce when wanted
-more convenient as either parent can feed
-parents don’t need to worry about what to eat
-doesn’t need to be fed as often

DISADVANTAGES

• cost
• lack of antibodies/immunity to baby
• harder to digest
• chemicals
• need access to clean water
• can stop production of breast milk

Question 29

Describe the methods of transmission of human immunodeficiency virus (HIV), and the ways in which HIV/AIDS can be prevented from spreading

Answer 29

Methods of transmission of HIV

• blood
• semen
• vaginal secretions
• breast milk

Activities that allow HIV transmission

• unprotected sexual contact
• direct blood contact, including injection drug needles, blood transfusions, accidents in health care settings or certain blood products.
• mother to baby (before/during birth) (through breast milk) - shared blood supply.

Prevention of HIV spreading

• protected sex
• if you inject drugs, don’t share needles/syringes
• don’t share razors, toothbrush or other items that may have blood on them
• if you’re a mother with HIV, don’t breast feed
• take medication according to your health provider’s directions.

Question 30

Outline how HIV affects the immune system in a person with HIV/AIDS

Answer 30

HIV uses the immune system to reproduce, making it unable to fight bacteria. You die of a common disease. HIV attacks and kills crucial immune system cells, known as T-helper cells. Without T-helper cells (which kills cell that have been infected with germs) many other immune system cells cannot work properly.

Question 31

Describe transport in plants

Answer 31

Transpiration: moves water and minerals from roots to leaves. Dead cells
Translocation at phloem: moves food substances from leaves to rest of the plant. Columns of living cells