Abiotic factors – Notes

1. Abiotic factors – Notes 1. Light (photo-): the intensity, colour, direction or duration 2. Gravity (geo-): organisms need to know ‘up’ and ‘down’, orientation 3. Temperature (thermo-): the average and the range 4. Water (hydro-): the humidity, soil moisture, speed of current, salinity, turbidity (cloudiness), depth, average rainfall 6. Chemicals (chemo-): inorganic nutrients, carbon dioxide, oxygen, salitness, pH, poisons, pheromones 7. Touch (thigmo-): a response to a solid object

2. Biotic Factors • These include the relationships between members of the same species (intraspecfic) and with members of other species (interspecfic).

3. Intraspecific Relations • Competition; food, resources, space, light, water and mates. • Aggressive interactions; territories, hierarchies. • Co-operative interactions; group formation for defense, and to help survival

4. Interspecific Relationships

5. Organism

6. Stimulus- a change in the environment (external or internal) that causes a response in an organism. • Receptor- any cell or group of cells that can detect this change. • Effector; a cell or group of cells that respond.

7. Response of organisms to the environment • The response of organisms to signals from the environment is called behaviour. • If the behaviour is genetic, we say the behaviour is innate. • If the behaviour is not genetic is is considered to be learned

8. Nature versus Nurture:Revisiting an Old Debate Nature Nurture • Behaviors are: • Innate • Hard-wired • Instinctual • Genetically determined • Behaviors are: • Learned • Flexible • Not genetically determined Behavior results from both genes and environmental factors

9. Introduction This topic is divided into three main headings: 1. Orientation responses to abiotic environment 2. Timing responses to abiotic environment and 3. Responses to biotic environment –relationships between organisms

10. 1. Orientation Responses PLANTS These will include: • Tropisms • Nastic responses • Taxes • Kineses • Homing • Migration When studying these responses you must look at the adaptive advantagesthat the population gains from them. You must also link the responses to the genetic make-up of the population and its possible evolution. ANIMALS Loggerhead and leatherback hatchlings are known to orient to the Earth's magnetic field: for these tests, each hatchling was placed into a nylon-Lycra harness.

12. PLANT MOVEMENTS • Plants are “rooted” to the spot • Time lapse photography : plants are capable of movements in response to environmental cues • Two main types of plant movements: • Tropisms • Nastic movements (Turgor) These are involuntary!! Plants don’t think! It’s just a response.

13. TROPISMS • A tropism is a directional growth response to an external stimulus and it may be positive (towards the stimulus) or negative (away from the stimulus) • Often caused by hormones • Types of Tropism • Phototropism • Geotropism (Gravitropism) • Thigmotropism • Hydrotropism • Chemotropism • The Thale Cress is regulated by blue to UV light

14. Phototropism • Directional growth response of a plant organ to a light stimulus This shoot is positively phototrophic

15. Shadedside ofshoot Light Illuminatedside ofshoot • Phototropism results from faster cell growth on the shaded side of the shoot than on the illuminated side

16. PHOTOTROPISM & AUXINS • Darwin’s experiments showed that coleoptiles only bend toward light when their tips are exposed. • Therefore – tip must contain photoreceptor • Bending takes place below the tip so message must travel from sensor area (tip) and elongating cells lower down(effector).

18. PHOTOTROPISM & AUXINS Boysen –Jensen confirmed that the light-activated substance in the tip was mobile Gelatin – permeable Mica – non-permeable

19. Chemical Messengers: Hormones • Hormone: • Chemical secreted in one part of a plant/animal and transported to target sites where it affects growth or activity

20. Shoot tip placed on agar block.Chemical (later called auxin)diffuses from shoot tip into agar. Agar Block withchemicalstimulatesgrowth. Other controls:Blocks with nochemical haveno effect. Offset blocks withchemical stimulatecurved growth. Control NO LIGHT HAND-OUT

21. Went concluded that a coleoptile curved toward light because its dark side had a higher concentration of the growth-promoting chemical, which he named auxin.

22. HOW DOES AUXIN WORK? • Stimulates cell elongation

23. GEOTROPISM (GRAVITROPISM) • Geotropism is the directional growth response of a plant organ to the stimulus of gravity • Roots – positively gravitropic • Shoot – negatively gravitropic • Even when the seed is planted underground in the dark

24. It may be caused by the settling of special organelles on the low sides of shoots and roots • This may trigger a change in the distribution of hormones • Gravitropism is a response to gravity Figure 33.9A

25. INVESTIGATING GRAVITROPISM Gravitropism / Geotropism The experiment below shows the effect of gravity on the growth of a seedling. After germinating, the young seedling (top) is turned on its side. Several days later (bottom), its roots have turned downwards and its shoot upwards in response to gravity.

26. Gravitropism is an important adaptation

27. GRAVITROPISM & AUXINS • The plant probably detects the direction of Earth’s gravitational pull through the sinking of starch granules • This somehow causes auxin to move to the bottom side of the growing tip

28. GRAVITROPISM & AUXINS • Auxin concentration may determine the direction of growth • Low concentrations of auxin stimulate root tip growth downward but inhibit shoot tip growth upwards • And vice versa • It ensures that the shoot will grow upward toward light and the roots will grow down into the soil, no matter how the seed lands in the soil

29. THIGMOTROPISM • Thigmotropism is the directional growth of plants in response to rubbing / touch on one side of a stem or tendril • Occurs in vines and other climbing plants Touched cells produce auxin & transport it to untouched cells. These will then elongate faster so growth bends around the object

30. It is responsible for the coiling of tendrils and vines around objects • It enables plants to use other objects for support while growing toward sunlight • Thigmotropism is a response to touch Figure 33.9B

31. HYDROTROPISM • Hydrotropism is a directional growth response in which the direction is determined by the gradient in water concentration • Difficult to observe for roots grown in soil” • Can’t observe without disturbing soil • Gravitropism is usually stronger than root hydrotropism • Root hydrotropism has been studied in humid air rather than soil • Roots cannot “sense” water & grow towards it!

32. CHEMOTROPISM • Directional growth in response to certain chemicals. • Eg. Pollen tube grows towards the ovary in the flower = chemotropism

33. NASTIC MOVEMENTS • The response of plant organs to diffuse stimuli that do not come from any particular direction • So response is independent of stimulus direction, unlike tropisms • Photonasty • thigmonasty • Thermonasty

34. Nastic Responses Nastic movements are plant movements that occur in response to environmental stimuli but unlike tropic movements, the direction of the response is not dependent on the direction of the stimulus.

35. Nastic Responses and Turgor Pressure • Turgor pressure is the force pushing against the cell wall due to the influx of water into the cell. It is the mechanism involved in turgor movements • Osmosis – movement of water from a high concentration to a low concentration through a semi-permeable membrane

36. TURGOR MOVEMENTS • Nastic Turgor – rapid, reversible movements resulting from turgor pressure changes within the cells • Not generally related to the direction of the stimulus

37. RAPID LEAF MOVEMENTS • Mimosa plant: When the sensitive leaves are touched they droop down & leaflets fold up • Very fast – takes about 1 sec • Due to loss of turgor pressure in specialized cells at joints of leaves & leaflets

38. Venus Fly Trap The Venus fly trap uses a similar mechanism to the Mimosa to shut its trap when a fly touches the sensitive hairs on its leaf

39. PHOTONASTY • A response to a change in light intensity • Does not include growth • Eg. Prayer Plant • Eg Evening Primrose flowers at dusk • Low light intensity is the stimulus

40. THERMONASTY • A response to change in temperature • Eg. Tulip

41. Discuss the response of Mimosa pudica to the sudden shock stimulus, and compare it to the plant’s growth response under a constant directional light source. In your answer: • identify and describe both the rapid leaf response and the slower growth response • explain how both the rapid leaf response and the slower growth response happen • compare and contrast both responses in terms of their significance to the plant’s survival.

42. OTHER RESPONSES TO LIGHT • Etiolation: • If a plant has reduced light or is grown in the dark it becomes etiolated • Leaves grow small & yellow & there are long internodes • Yellow colour comes from pigment protochlorophyll, which needs light to turn it into green chlorophyll

43. ETIOLATION • These are morphological adaptations for growing in darkness • Collectively referred to as etiolation

44. Etiolation of a Potato After a week’s exposure tonatural daylight. The potatoplant begins to resemble a typical plant with broad greenleaves, short sturdy stems, and long roots. This transformationbegins with the reception oflight by a specific pigment,phytochrome.

45. Animal Orientation Responses • Fall into 4 categories : • Taxes; a directional response towards or away from the directional stimulus • Kineses;a non-directional response in which the rate of turning or movement is related to the intensity of the stimulus • Migrations-Seasonally repeated mass movements of a species from a breeding area to a feeding area (and usually back again unless animal only lives to breed once) • Homings; A journey from a foraging area back to a home base (over some familiar territory )

46. TAXIS • Plural = taxes • Movement of the whole organisms towards or away from a directional stimulus • Occur in animals, algae or bacteria

47. KINESIS • The change in rate of movement of the whole organism in response to the change in intensity of a non-directional stimulus • Are NOT said to be positive/negative as the stimulus is not directional • Orthokinesis: The speed of the movement is related to the intensity of the stimulation • Klinokinesis: The amount of random turning is related to the intensity of the stimulation

48. MIGRATION • The annual mass movement of organisms from an area where they breed to an area where they do not breed • Usually involves the return journey • Occur in animals only

49. MIGRATION • True migration – “round trip” – the return to the original breeding site from the over-wintering site completes the journey • Triggers to migration: • Drop in temperature • Days becoming shorter • Genetic drive that is innate (inbuilt)

50. Why Migrate???