How does phototropism occur in plants

Q. No. 6: How does phototropism occur in plants?

Ans: Environmental triggers such as light will change the directions that plant parts grow in. These directional, or tropic, movements can be either towards the stimulus, or away from it. So, in two different kinds of phototropic movement, shoots respond by bending towards light while roots respond by bending away from it. 

Draw the structure of a neuron and explain its function

Q. No. 5: Draw the structure of a neuron and explain its function.

Ans: Neurons are nerve cells which are the functional units of the nervous system. The three main parts of a neuron are dendrite, cell body and axon.

Structure of neuron

Functioning of its three parts.

Dendrite: It detect information and conducts the messages towards the cell body.

Cell body: It contains nucleus, mitochondria, and other cell organelles. It maintains the growth of the cell.

Axon: It conducts messages away from the cell body and pass to the next neuron.

What is the function of receptors in our body

Q. No. 4:  What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?

Ans: Receptors are present in our all parts of the body for example in skin, eye, nose tongue etc. They detect the signals and then send them to brain in the form of electrical signals. If they these receptors are damaged then it they will not detect the input which leads to the harm for our body in dangerous situation.

The brain is responsible for thinking or

Q. No. 3: The brain is responsible for

(a)  thinking.

(b)  regulating the heart beat.

(c)  balancing the body.

(d)  all of the above.

Ans: (d) all of the above 

Which of the following is a plant hormone

Q. No. 1: Which of the following is a plant hormone?

(a)  Insulin

(b)  Thyroxin

(c)  Oestrogen

(d)  Cytokinin

  Ans:  (d) Cytokinin is a plant hormone. 

The gap between two neurons is called a

Q. No. 2: The gap between two neurons is called a

(a)  dendrite.

(b)  synapse.

(c)  axon.

(d)  impulse.

Ans:  (b) The gap between two neurons is known as synapse. 

How does our body respond when adrenaline is secreted into the blood

Q. No. 3: How does our body respond when adrenaline is secreted into the blood?

Ans: When someone is in danger or in emergency then adrenal gland secrete adrenaline hormone. It is secreted directly into the blood and is transported to different parts of the body. It speeds up the heartbeat and hence supplies more oxygen to the muscles. This results in increasing breathing rate and blood pressure which enable them to fight with such urgent situation.

Why are some patients of diabetes treated by giving injections of insulin

Q. No. 4: Why are some patients of diabetes treated by giving injections of insulin?

Ans: Insulin is a hormone secreted by pancreas that regulates the sugar level in the blood. When this hormone is not synthesised in proper amount then the sugar level in the blood rises and the persons suffer from diabetes.

This is the reason why diabetic patients are treated by giving injections of insulin.

Why is the use of iodised salt advisable

Q. No. 2: Why is the use of iodised salt advisable?

 Ans: Iodine is needed by the thyroid gland for the production thyroxin hormone. This hormone regulates fat, protein and carbohydrate metabolism in our body. If this is in deficient quantity then the neck will swell up due to the enlargement of thyroid gland. This deficiency disease is known as goitre.

Therefore the iodised salt is advised.

Design an experiment to demonstrate hydrotropism

Q. No. 5: Design an experiment to demonstrate hydrotropism.

Ans:  Take a cubical transparent glass container and fill it with water. Now put some geminating seeds in it. After one or two days you will observe that the roots of all the geminating seeds will grow towards the water. This experiment proves that roots of germinating seed show the character of positive geotropism.

How does chemical coordination take place in animals

Q. No. 1: How does chemical coordination take place in animals?

 Ans: Chemical coordination takes place in animals with the help of hormones. Hormones are the chemical fluids that are secreted by the glands of the endocrine system. Hormones regulate the overall growth and development of the animals.

Give an example of a plant hormone that promotes growth

Q. No. 3: Give an example of a plant hormone that promotes growth.

Ans: Gibberellin is an example of plant hormone which promotes the growth of the plant.

How do auxins promote the growth of a tendril around a support

Q. No. 4: How do auxins promote the growth of a tendril around a support? 

Ans: Auxin is plant hormone which is synthesized at the tip of the shoot. It helps the cell grow longer. When a tendril comes in contact with a support, auxin stimulates faster growth of the cells on the opposite side that’s why the tendril forms a coil around the support.

How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light

Q. No. 2: How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?

Ans: The movements of the leaves of the sensitive plant are touch sensitive and independent of growth. While the movement of the shoot towards light is growth related and known as phototropism.

What are plant hormones

Q. No. 1: What are plant hormones?

 Ans: Plant hormones are the fluids which are secreted within the plant also known as phytohormones. Plant hormones regulate the growth and development of the plant. Examples of plant hormones are auxin, gibberellins etc.

What is the role of the brain in reflex action

Q. No. 5: What is the role of the brain in reflex action?

Ans: Reflex actions are sudden responses. It is involuntary action which does not involve thinking. For example, when we touch a hot object, we withdraw our hand immediately without thinking.  The sensory nerves that detect the heat are connected to the nerves that move the muscles of the hand. Such a connection of detecting the signal from the nerves (input) and responding to it quickly (output) is known as reflex arc. Reflex arcs are formed in the spinal cord and the information reaches the brain and the brain responses to it.

reflex action

How do we detect the smell of an agarbatti (incense stick)

Q. No. 4: How do we detect the smell of an agarbatti (incense stick)?

Ans: when the smell of the incense stick reaches to our nose then the olfactory receptors present in our nose detects it send this information in fore brain in the form of electrical signals. Fore brain interprets this information as the smell of incense stick where it is already stored. 

Which part of the brain maintains posture and equilibrium of the body

Q. No. 3: Which part of the brain maintains posture and equilibrium of the body?

Ans: Cerebellum, which is a part of hind brain and is responsible for maintaining posture and equilibrium of the body.

What is the difference between a reflex action and walking

Q. No. 1: What is the difference between a reflex action and walking?

Ans:  A reflex action is voluntary action which is a rapid and automatic response to stimuli. While walking is a voluntary action which requires our thinking and in our control.

What happens at the synapse between two neurons

Q. No. 2: What happens at the synapse between two neurons?

Ans: A synapse is the gap between the two neurons. At synapse the electrical signals converted into chemicals that can easily cross over the gap and pass on to the next neurons where it again converted into electrical signals.

Explain how rusting of iron is envisaged as setting up of an electrochemical cell

Q3.15: Explain how rusting of iron is envisaged as setting up of an electrochemical cell .

Solution:

In process of rusting, water molecules present at the layer of iron react with oxides and get dissociated and give H⁺ ions

 H₂O + CO₂   →        H₂CO₃

H₂CO₃                                ↔        2H⁺                 +          CO₃^2–

In present of H⁺ ions iron convert in Fe²⁺so this part is act as anode

Reaction at anode:

Fe(s)               →        Fe²⁺(aq)         +          2e^–

Electron released at anodic spot move through the metals and go to another spot on the metal and reduce oxygen this spot act as cathode

Reaction at Cathode:

O₂(g)   +  4H⁺(aq)  +  4e⁺( aq)          →        2H₂O(l)

The overall reaction

2Fe(s)  + O₂(g)    +    4H⁺(aq)          →        2H₂O(l)  + Fe²⁺(aq)

Hence, rusting of iron act as electrochemical cell.

Suggest two materials other than hydrogen that can be used as fuels in fuel cells

Q3.14: Suggest two materials other than hydrogen that can be used as fuels in fuel cells.

Solution:

Products are

(1)Methane (CH4)

(2)Methanol (CH3OH)

What is the quantity of electricity in coulombs needed to reduce 1 mol of Cr2O72– given that Consider the reaction: Cr2O72– + 14H+ + 6e– → 2Cr3+ + 8H2O

Q3.12: Consider the reaction:

Cr₂O₇^2–+ 14H⁺ + 6e^– → 2Cr³⁺ + 8H₂O

What is the quantity of electricity in coulombs needed to reduce 1 mol of Cr₂O₇^2– ?

Solution:

In given equation there are 6 electrons are required so that n = 6

Use the formula

Required charge      = nF

Plug the values in this formula we get

Required charge      = 6 × 96487 Coulombs

= 578922 Coulombs

= 5.79 × 10⁵ Coulombs

Suggest a list of metals that are extracted electrolytically

Q3.11: Suggest a list of metals that are extracted electrolytically.

Solution:

The Metals which is at the top of the reactivity series  can extracted electrolytically.

So all alkali metals and some alkaline metals can extracted with this method\

Example Li, Na, K, Mg, Al etc.

If a current of 0.5 ampere flows through a metallic wire for 2 hours, then how many electrons would flow through the wire?

Q3.10: If a current of 0.5 ampere flows through a metallic wire for 2 hours, then how many electrons would flow through the wire?

Solution:

Current, I = 0.5 A

Time, t = 2 hours

 Convert in sec we get

Time, t = 2 × 60 × 60 s

 = 7200 s

Use formula

Charge           Q = It

Plug the values we get

                            = 0.5 A × 7200 s

    = 3600 Coulombs

Number of electrons = total charge / charge on 1 electrons

                                     = 3600/(1.6 ×10 ¹⁹)

                                     =2.25 × 10²² electrons  

The molar conductivity of 0.025 mol L−1 methanoic acid is 46.1 S cm2 mol−1. Calculate its degree of dissociation and dissociation constant. Given λ0(H+)= 349.6 S cm2 mol–1 and λ0(HCOO–) = 54.6 S cm2 mol–1

Q3.9:  The molar conductivity of 0.025 mol L−1 methanoic acid is 46.1 S cm² mol⁻¹. Calculate its degree of dissociation and dissociation constant. Given λ⁰(H⁺)= 349.6 S cm² mol^–1 and λ⁰(HCOO^–) = 54.6 S cm² mol^–1

Solution:

Given that

λ⁰(H⁺)= 349.6 S cm² mol^–1

λ⁰(HCOO^–) = 54.6 S cm² mol^–1

Concentration ,C = 0.025 mol L⁻¹

λ(HCOOH) = 46.1 S cm² mol⁻¹

use formula

λ^o(HCOOH)   = λ⁰(H⁺)  +   λ⁰(HCOO^–)

plug the values we get

λ^o(HCOOH)   = 0.349.6 + 54.6

                        =404.2 S cm² mol⁻¹

Formula of degree of dissociation:

ά = λ^o(HCOOH)/ λ^o(HCOOH)

ά = 46.1 / 404.2

ά = 0.114

Formula of dissociation constant:

K = (c ά²)/(1 – ά)

Plug the values we get

K = 3.67 × 10^–4 mol per liter 

Suggest a way to determine the Λom value of water

Q3.8: Suggest a way to determine the Λ^o_mvalue of water.

Solution:

According to Kohlrausch’s law

Λ^o_m(H2O)  = Λ^o_m(HCl) + Λ^o_m(NaOH) – Λ^o_m(NaCl)

Hence if we know the values of Λ^o_m  for  HCl, NaOH, and NaCl, then we can calculate the value of Λ^o_m  for the water

Why does the conductivity of a solution decrease with dilution

Q3.7: Why does the conductivity of a solution decrease with dilution?

Solution:

The conductivity of a solution is directly proportional to number of ions present in a unit volume of the solution because current is carried forward by the ions. With dilution number of ions in unit volume decreases so that conductivity also decreases. Hence with dilution conductivity decreases 

The cell in which the following reactions occurs Calculate the standard Gibbs energy and the equilibrium constant of the cell reaction

Q3.6: The cell in which the following reactions occurs:

Calculate the standard Gibbs energy and the equilibrium constant of the cell reaction.

Solution:

Given that

n     = 2

T     = 298 K

E^o_cell =  0.236 V

We have the formula

∆_rG^θ = – nFE^o_cell   

Plug the values, we get

∆_rG^θ = −2 × 96487 × 0.236

∆_rG^θ = −45541.86 J mol⁻¹

Divide by 100o to convert in KJ

∆_rG^θ = −45.54 kJ mol⁻¹  

Use second formula of ∆_rG^θ

∆_rG^θ =−2.303RT log K_c

Plug the values we get

 −45541.86 J mol⁻¹ = –2.303 × 8.314 × 298  log K_c

Solve it we get

Log K_c  = 7.98

Take antilog both side, we get

K_c      = Antilog (7.98)

= 9.6 × 10⁷